Methods and systems for in-situ leakage current testing of cells in multi-cell battery packs

ABSTRACT

Described methods and systems provide in-situ leakage current testing of battery cells in battery packs even while these packs operate. Specifically, an external electrical current is discontinued through a tested battery cell using a node controller, to which the tested battery cell is independently connected. Changes in the open circuit voltage (OCV) are then detected by the node controller for a set period time. Any voltage change, associated with taking the tested cell offline, is compensated by one or more other cells in the battery pack. The overall pack current and voltage remains substantially unchanged (based on the application demands), while the in-situ leakage current testing is initiated, performed, and/or completed. The OCV changes are then used to determine the leakage current of the tested cell and, in some examples, to determine the state of health of this cell and/or adjust the operating parameters of this cell.

BACKGROUND

Multi-cell battery packs are used for various applications. Whileindividual battery cells, forming a pack, typically have the samedesign, these cells may exhibit some differences in performancecharacteristics, such as self-discharge. Self-discharge is an inherentcharacteristic, which can be influenced by manufacturing, age, cyclingparameters, temperatures, and others. Specifically, self-discharge iscaused by an internal leakage current, which comes from limits onelectric insulation between the two electrodes in the cell.Self-discharge variations (e.g., among different cells in the samebattery pack and/or change for the same cell after some time) may beused to monitor the state of health and/or the state of safety of thecells and the overall battery pack. Furthermore, in some examples,self-discharge variations may potentially cause a state of charge (SOC)imbalance, e.g., for nickel-metal hydride and nickel-cadmium cells.

While accurately measuring self-discharge of cells in battery packs isdesirable, this type of measurement is very challenging and typicallynot possible when the battery packs are in operation. Accuratemeasurement of a cell leakage current requires taking this cell offlineand not passing any external current through the cell, often for aprolonged time. Conventional battery packs do not allow taking cellsoffline, e.g., when the pack is charged or discharged, which may bereferred to as in-situ testing. At the same time, many applications ofbattery packs (e.g., electric vehicles, grid energy storage) may preventtaking the entire battery pack offline to measure the leakage current ofindividual cells, which may be referred to as offline testing. Manyapplications prevent prolonged and predictable offline modes.Furthermore, conventional battery management systems (BMS) connected tocells in battery packs often load the cells with a quiescent currentthat is larger than the leakage currents of the cells. Self-discharge isalso typically different for different SOCs and/or other conditions,such as temperature. Accounting for these conditions is far beyond thecapabilities of conventional BMS. Furthermore, conventional BMS are notcapable of identifying individual unsafe cells or, more specifically,identify specific degradation modes of individual cells (e.g., based onleakage current results). Finally, bringing an off-line cell back onlineis challenging and typically requires SOC balancing with other cells,which is also beyond the capabilities of conventional BMS.

What is needed are novel methods and systems for in-situ leakage currenttesting of battery cells in multi-cell battery packs.

SUMMARY

Described methods and systems are used for in-situ leakage currenttesting of battery cells in battery packs even while these packsoperate. Specifically, an external electrical current is discontinuedthrough a cell using a node controller, to which this tested cell isindependently connected. Changes in the open circuit voltage (OCV) aremonitored to determine the leakage current of this cell. Changes in acell's contribution to a pack's voltage and power output, associatedwith taking the tested cell offline, is compensated by one or more othercells in the pack. The overall pack voltage remains substantiallyunchanged while the tested cell is taken offline and later when the cellis brought back online. The leakage current data is to determine thestate of health, state of safety, and/or one or more degradation modesof this cell and, in some examples, to adjust the operating parametersof this cell.

In some examples, a method for in-situ leakage current testing ofbattery cells in a battery pack is provided. The method comprisesdiscontinuing an external cell current through a first battery cell of afirst battery node while the battery pack remains operational andproviding power output. The method further comprises determining leakagecurrent of the first battery cell based on cell data obtained from thefirst battery cell.

In some examples, a battery pack, configured for in-situ leakage currenttesting of battery cells in the battery pack is provided. The batterypack comprises a first battery node, comprising a first node controllerand a first battery cell, electrically coupled to the first nodecontroller. The first node controller is configured to discontinue anexternal cell current through the first battery cell while the batterypack remains operational and providing power output. The battery packalso comprises a second battery node, comprising a second nodecontroller and a second battery cell, electrically coupled to the secondnode controller. The battery pack comprises a bus, electricallyinterconnecting the first node controller and the second nodecontroller, and a battery pack controller, communicatively coupled tothe first node controller and the second node controller. At least oneof the first node controller or battery pack controller is configured todetermine leakage current of the first battery cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic block diagram of a battery ecosystem, used forcollecting and analyzing battery data from multiple power systems anddeveloping new battery operating procedures and/or new battery testingprotocols for these power systems, in accordance with some examples.

FIG. 1B is a schematic block diagram of a battery pack, comprisingmultiple battery nodes, interconnected in series and controlled by abattery pack controller, in accordance with some examples.

FIG. 1C is a schematic block diagram of another example of a batterypack, comprising multiple battery nodes, interconnected in series andcontrolled by a battery pack controller.

FIG. 1D is a schematic block diagram of a node controller, used in eachnode of a battery pack, in accordance with some examples.

FIG. 1E is a schematic block diagram of a battery pack controller,showing various components and features, used by the battery packcontroller to control operations of each node in a battery pack, inaccordance with some examples.

FIG. 2A is a process flowchart corresponding to a method for collectingand analyzing battery data from multiple power systems and developingnew battery operating procedures and/or new battery testing protocolsfor these power systems, in accordance with some examples.

FIG. 2B is a process flowchart corresponding to a method for an in-situleakage current testing of battery cells in a battery pack, inaccordance with some examples.

FIGS. 2C-2E are schematic block diagrams illustrating different examplesof a battery pack while testing a first battery cell for leakagecurrent.

FIG. 3A illustrates node and pack voltages showing power changes on onenode compensated by another node, in accordance with some examples.

FIG. 3B illustrates node and pack voltages showing no power changesacross the node, in accordance with some examples.

FIG. 3C illustrates cell currents and a node voltage showing a powercompensation example within the node.

FIG. 4A is an example of measuring OCV changes of a battery cell todetermine leakage current.

FIG. 4B is an example of a leakage current profile as a function of theSOC.

FIG. 4C is an example of a leakage current profile as a function of thetemperature.

FIGS. 5A-5D are various leakage current profiles corresponding tolithium plating events, in accordance with some examples ofdegradation-mode determination protocols.

FIGS. 6A-6B are two leakage current profiles corresponding to internalshort events, in accordance with some examples of degradation-modedetermination protocols.

FIGS. 7A-7B are various leakage current profiles corresponding togassing events, in accordance with some examples of degradation-modedetermination protocols.

DETAILED DESCRIPTION

In the following description, numerous specific details are outlined toprovide a thorough understanding of the presented concepts. In someexamples, the presented concepts are practiced without some or all ofthese specific details. In other instances, well-known processoperations have not been described in detail to not unnecessarilyobscure the described concepts. While some concepts will be described inconjunction with the specific examples, it will be understood that theseexamples are not intended to be limiting.

INTRODUCTION

Self-discharge is an inherent characteristic of battery cells, caused byinternal electrical currents within these cells. These internal currentsare also referred to as leakage currents, which are used to characterizeself-discharge. While leakage currents are not desirable, they are oftenunavoidable. Furthermore, leakage currents can change over time (e.g.,as battery cells age). Finally, detecting leakage currents can bechallenging.

In some examples, leakage currents vary among cells in the same batterypack. For example, battery cells of the same type (e.g., the samedesign, chemistry, and manufacturer) may have different leakage currentcharacteristics resulting from unintended variations in materials,assemblies, and testing. Furthermore, different cells in the samebattery pack may be subjected to different operating conditions (e.g.,temperature, SOC) resulting in different levels of degradation, whichaffects the leakage current characteristics. The leakage current is amajor indicator of the cell's degradation or lack thereof, which may bereferred to as a cell's state of health (SOH) and which is alsoindicative of a cell's state of safety (SOS). The leakage current, ifidentified with sufficient precision and at certain cell conditions(e.g., temperature, SOC), can provide a strong indication of differentdegradation modes (or, more specifically, failure modes) of the cell,such as internal mechanical shorts, gas evolution on positiveelectrodes, irregularities on solid electrolyte interface (SEI) layers,metal dendrite formations on negative electrodes, and others. In someexamples, a specific degradation mechanism and/or a failure mode of thecell can be identified from the corresponding leakage current data.

In some examples, the leakage current of a cell is detected based on OCVchanges over time, often a relatively long time. The leakage currentcauses the cell to self-discharge, thereby reducing the SOC of the cell.As the SOC drops, the OCV of the cell also changes. As such, todetermine the leakage current based on OCV changes, the cell is takenoffline such that no external currents pass through the cell, and two ormore OCV measurements can be performed. In some examples, the cell istaken offline for a substantial time (e.g., at least one day, at leastone week) while the battery pack remains operational. This perioddepends on the leakage current, desired test accuracy, equipmentprecision, and other factors (e.g., types of cell, temperature, SOC).For example, a typical lithium-ion cell exhibits a 1%-10% drop in theSOC in the first 24 hours after being fully charged due to therelaxation effect, corresponding to an equivalent leakage current ofabout 10⁻³ C to 10⁻² C. The SOC drop then reduces to 1-2% per month,corresponding to the leakage current of between about 10⁻⁴ C to 10⁻⁵ C(with 1 C corresponding to a cell being charged from 0% SOC to 100% SOCin 1 hour). However, OCV values may only change by 10⁻³V to 10⁻²V over1-10 days, especially for cells with low leakage currents (e.g., newcells). One having ordinary skill in the art would understand that thevalues presented above are for illustration purposes only and are notintended to be limiting. Overall, leakage current testing may take longperiods and precise equipment for monitoring OCV. While the currentdisclosure focuses on OCV monitoring as an example of determiningleakage current, other methods of leakage current testing are alsowithin the scope. In another example, a cell in a selected SOC (e.g., afully charged state or some intermediate SOC, which is known withsufficient precision) is disconnected for some time, after which thecell is charged back to this selected SOC. The charge amount needed tobring the cell back to the fully charged state (or other precisely knownintermediate SOC) indicates the leakage current. In another example, acell is maintained at a constant voltage or, more specifically, aselected SOC, by supplying a small amount of current to the cell, whichmay be referred to as a recharging current. This amount of rechargingcurrent corresponds to the leakage current.

At the same time, most conventional battery applications and batterypack designs do not allow isolating individual cells for long periods,which may be needed for leakage current testing (e.g., OCV monitoring).For example, even if a battery pack is idle, certain connections inconventional battery packs (e.g., parallel connections) may limit OCVmonitoring of individual cells. Aggregate leakage current data (e.g.,from multiple cells) does not allow assessing the SOH of individualcells with sufficient precision. Furthermore, predicting the duration ofa battery pack being idle (i.e., not operational) is often not possible,while restricting the battery pack operations for prolonged periods maynot be feasible. This problem with conventional battery packs becomeseven more complex when OCV monitoring is required at a particular SOC,which may be needed for determining specific degradation modes. Forexample, it may not be possible to determine when a battery pack will beat a certain SOC and, at the same time, will not be operational for aprolonged period, as may be required for leakage current testing.

Described methods and systems allow in-situ leakage current testing ofindividual battery cells in battery packs. For purposes of thisdisclosure, “in-situ testing” is defined as testing performed while thebattery pack remains operational and continues to operate, e.g., beingcharged or discharged to receive charging power or provide power outputto an external load. In-situ testing should be distinguished fromoffline testing, e.g., when the entire battery pack is taken offline andis not operational (e.g., disconnected from the external load).

In some examples, the in-situ testing is performed without any changesto the overall pack operation parameters (e.g., to the pack voltageand/or to the pack power output). Specifically, during the in-situleakage current testing, one or more cells are taken offline for leakagecurrent testing, while the pack continues to operate in a similar manner(e.g., as demanded by the external load). The power contributions ofthese tested cells (to the overall pack power output) may be compensatedby one or more other cells in the pack. These other cells are operatedper specific compensation profiles, which may be also referred to as apower compensation profile. As a result, the battery pack continues tooperate without any disruptions (e.g., providing the same level ofpower). It should be noted that the pack voltage and current may bevaried during testing even though the power output remains the same. Itshould be noted that the SOC, power, voltage, and/or current of thebattery pack may change while performing in-situ leakage currenttesting, e.g., based on different power demands from the battery pack.However, these changes are driven by the application requirement of thebattery pack (e.g., power demands) rather than by in-situ leakagecurrent testing. It also should be noted that taking one or more cellsoffline (for in-situ leakage current testing) and then bringing thesecells back online (after completing the in-situ leakage current testing)does not impact the overall operation of the battery pack.

When one or more battery cells are taken offline and tested, no chargeor discharge currents are applied to these tested cells. In other words,the external cell current through each of the tested cells isdiscontinued. This external cell current should be distinguished fromthe leakage current, which is internal to the cell and generally cannotbe controlled, at least not in the same manner as the external cellcurrent. The external cell current should be also distinguished from atest current, which may be used for leakage current testing (e.g.,charging a tested cell with a current equivalent to a leakage current tomaintain the same SOC of the tested cell). The external cell currentcontributes to the power output of the battery pack while the packcharges or discharges.

In some examples, once one or more battery cells are taken offline bydiscontinuing external currents through these cells, two or more OCVmeasurements are taken for each of these tested cells over a time periodto determine the leakage current of this cell. In more specificexamples, multiple OCV measurements are taken, e.g., to establish an OCVprofile or a time series. In some examples, the duration of the test isinitially unknown. Instead, the duration is dynamically establishedbased on the measured OCV changes and the desired test precision.Furthermore, in some examples, in-situ leakage current testing isrepeated for different SOCs, different cell temperatures, and/or otherlike factors. In some examples, the process may involve capturing atemperature profile corresponding to a captured OCV profile, e.g.,measure both the OCV and temperature of the cell over a test period.Furthermore, the temperature profile is taken into account whenanalyzing the OCV profile. The effects of temperature on the leakagecurrent are described below with reference to FIG. 4C.

When a battery cell is taken offline (i.e., removed from the operationof the battery pack and tested with no external cell current passingthrough the battery cell), the battery cell stops contributing to thetotal power output of the battery pack. While various references aremade to “power output” of a battery pack/cell, one having ordinary skillin the art would understand that this term encompasses both the powersupplied and the power received by the battery pack/cell. For example,in-situ leakage current testing may be performed while charging or whiledischarging the battery cell. Furthermore, the overall operationcontinuity during individual cell testing may be expressed in terms ofthe pack voltage, which remains substantially the same while changingthe current through one or more battery cells.

As noted above, the change in the power output contribution from thetested cell is offset and compensated by one or more other cells in thebattery pack. These one or more cells may be referred to as powercompensating cells and may include cells from the same nodes (as thetested cell) and/or different nodes. As such, during in-situ leakagecurrent testing, a battery pack includes one or more tested cells andone or more power compensating cells. In more specific examples, thebattery pack also includes one or more other cells, which are neithertested nor used for power compensation. These other cells may bereferred to as regular operating cells. Alternatively, all cells thatare not tested for leakage current are compensating cells, e.g., equallydistributing the power compensation.

It should be noted that the leakage current testing of a particular cellmay be initiated based on various triggers. Some examples of these testtriggers include, but are not limited to, operating history (e.g.,reaching or exceeding one or more operating limits, such as cut offvoltages and/or charge rates) of this cell or of the pack as a whole(e.g., after a high rate charge or discharge, after being exposed tohigh temperature), test history (e.g., previous leakage current and/orother data, identified degradation modes and severity of thesedegradation modes) of this cell or the pack as a whole, currentconditions of the cell and/or the power pack (e.g., SOC, temperature,OCV, voltage under a certain load), data analysis (e.g., of test andother data from battery cells equivalent to first battery cell 114), andother like trigger points. For purposes of this disclosure, equivalentbattery cells are defined as cells with the same design (e.g.,materials, form-factor) or at least the cells sharing one or more commoncharacteristics (e.g., materials). For example, a leakage currenttesting is triggered after a high-rate charge of the cell, upon reachinga certain SOC (e.g., at least 90%). In more specific examples, theminimum SOC threshold is used, e.g., because the leakage current is moredetectable at the higher SOC. Furthermore, a cell with a high SOC hasenough remaining capacity when the cell is brought back online and usedto supply the power to the power pack. Furthermore, the leakage currentmeasurement at a high SOC (at least 90% of the maximum operatingcapacity) may be used to determine specific degradation mechanisms asfurther described below. Testing may be performed at a specific SOCcorresponding to a tested degradation mode.

Some examples of these degradation mechanisms include, but are notlimited to, oxidation on positive electrodes, reduction on negativeelectrodes (e.g., gassing), and/or presence or development of mechanicalshorts in the cell (e.g., dendrites, loose particles). Other degradationmechanisms include dissolution and/or cracking of negative electrodesubstrates, corrosion of positive electrode substrates, loss of contactwith negative electrode substrates and/or positive electrode substrates,SEI decomposition and precipitation, excessive SEI formation, crackingof active material particles, the formation of cathodic surface films,polymer binder decomposition, and others. As further described below,these results may be used for various purposes, e.g., changing frequencyof future tests, performing different types of test schedule,service/maintenance/replacement of the battery pack, permanently ortemporarily bypass the cell, changing operating parameters of the cell,the node, and/or the pack, such as cut off voltages and/or charge rates.In some examples, operating parameters may be also referred to asoperating limits (e.g., maximum charge/discharge rates).

For example, in a lithium-ion cell, a standard discharge corresponds tolithium ions de-intercalating from the negative electrode, migrating tothe positive electrode through the separator and intercalating into thepositive electrode, as represented by the following formulas:Li₂C₂O₄+Y*Li_(x)C₆→2CO₂+2Li⁺+Y*Li_(x-2/Y)C6+2e−(negative electrode)2CO₂+2Li⁺+Z*Li_(W+2/Z)MO₂+2e−→Li₂C₂O₄+Z*Li_(W)MO₂(positive electrode)The process is reversed during a charge. At the same time, electronstravel through the external load, with a 1-to-1 ratio between thelithium-ion transfer and the electron transfer.

During a self-discharge, there is no external pathway for the conductionof electrons. Instead, a shuttle mechanism takes place internallybetween the two electrodes. For instance, decomposition byproduct (CO₂)of the oxidation of electrolyte at the positive electrode can migrate tothe negative electrode. Upon reaching the negative electrode, thisbyproduct is reduced in a reaction that consumes two lithium ions andtwo electrodes from the negative electrode, as represented by thefollowing formula:2CO₂+2Li⁺+Y*Li_(x-2/Y)C6+2e−→Li₂C₂O₄+Y*Li_(x)C6The byproduct (Li₂C₂O₄) of this reduction reaction then migrates to thepositive electrode where this byproduct gets oxidized and provides twoLithium ions and two electrons to the positive electrode, as representedby the following formula:Li₂C₂O₄+Z*Li_(W)MO₂→2CO₂+2Li₊+Z*Li_(W+2/2)MO₂+2e−One having ordinary skill in the art would understand that the abovedescription represents a general framework of self-discharge withinlithium-ion cells.

In some examples, an SEI layer is damaged (e.g., due to hightemperature, high-rate charge/discharge operations). When the SEI layeris damaged, highly reactive particles of the negative electrodes (in thedamaged portion) are exposed to and interface the electrolyte. Theelectrolyte gets reduced at this interface with the negative electrodeto form a fresh SEI layer, effectively to repair the damaged area. Inthis reduction/repair reaction, lithium ions and electrons are sourcedfrom the negative electrode as represented by the following formula:Electrolyte(liquid)+Li₊+Y*Li_(x-1/Y)C6+e−→SEI(solid)+Y*Li_(x)C6A decrease in the lithium concentration in the negative electrode raisesthe potential of the negative electrode, which in turn translates into adecrease in the OCV of the cell, which can be measured. As such, in someexamples, the OCV decrease is an indication of an SEI damage/repairprocess.

In some examples, when the lithium metal plates on the negativeelectrode, a portion of electrolyte interfaces highly reactive metalliclithium. The electrolyte gets reduced at the interface with the metalliclithium to form a new SEI layer to passivate the surface of the platedlithium. In this reduction reaction, presented below, lithium ions andelectrons are sourced from the plated lithium and represented by thesame formula as the one. As with the SEI layer damage, there is adecrease in the lithium concentration in the negative electrode, whichin turn translates into a decrease in the OCV of the cell, which can bedetected using the methods and systems described herein. Variousexamples of degradation mode detection are described below withreference to FIGS. 5A-7B.

In some examples, when lithium plating reaches a certain level, lithiumdendrites form on the negative electrode. At a certain size, the lithiumdendrites can pierce through the separator and create an electricallyconductive bridge between the two electrodes, which allows electrons toflow from the negative electrode to the positive electrode within thecell. When electrons are transferred in that manner, lithium-ionsde-intercalate from the negative electrode, migrate toward the positiveelectrode and intercalate into the positive electrode. This overallprocess corresponds to the drop in the SOC, which is evident from theOCV decrease and which can be detected during in-situ leakage currenttesting. In some examples, internal shorts are caused by variousparticles or debris inside the cell, e.g., current collector burrs,electrode flakes, and others. Furthermore, in some examples, internalshorts are caused by mechanical damage and/or an over-pressure event,which causes direct contact to be established between both electrodes bycompressing the separator. In some examples, the external terminals of acell are shorted externally, which creates an electrically conductivebridge between the two electrodes, like the internal shorts describedabove.

Overall, repeated testing of leakage current at different cellconditions (e.g., SOC, temperature, etc.) on individual cells can assistin the early detection of different degradation mechanisms. The earlydetection allows implementing various mitigation plans, such asscheduling predictive maintenance operations and/or determining newoperating parameters at the individual cell level. For example, leakagecurrent may be used to determine when certain cells and/or nodes shouldbe kept offline (e.g., completely bypassed) even after completion ofin-situ leakage current testing and during operations. Morespecifically, if a measured leakage current for a cell is larger than aset threshold, then the cell is first controllably discharged and takenoffline. Alternatively, a test result may be used to determine lessstressful operating parameters (e.g., reduced current rates and powerlevels, different cut off voltages) for one or more cells in the batterypack. In some examples, each cell may be operated according to itsindividual set of operating parameters, which are developed and updatedbased on periodic in-situ leakage current testing of this cell.

The results of leakage current testing may be used at a pack level,e.g., by a battery pack controller, to adjust operating parameters ofthe tested cell. Furthermore, the results may be shared in a batteryecosystem and collectively used together, e.g., with data from otherbattery packs/across a fleet of power systems comprising battery packs,equivalent to the battery pack with the tested cell. For example, abattery pack may be a part of a power system (e.g., an electric vehicle,a power backup system). Each power system may contain one or morebattery packs. The power system, or the battery pack directly, maysupply various battery data (e.g., results of leakage current testing)to a central battery data store. The aggregate data in this centralbattery data store is collectively analyzed to determine various globaltrends and anomalies, identify specific design concerns, pinpointproduction batches with potential defects, and other purposes. Thisglobal data analysis may be referred to as a big data analysis becausethis analysis involves data across multiple battery packs. This analysismay yield various new battery operating protocols and/or battery testingprotocols. Furthermore, the analysis may yield various recommendationsrelated to battery designs (e.g., materials, construction, and others).Additional examples of global data analysis are described below withreference to FIG. 2A.

Battery Ecosystem Examples

As noted above, multiple battery cells are often assembled into abattery pack to provide higher power output and/or higher energy storagecapacity. Battery packs, in turn, are often used as parts of varioushigher-level power systems, such as electric vehicles, stationary energystorage systems, grid balancing systems, and others. In some examples,one power system comprises multiple battery packs.

Many modern power systems have communication capabilities for receivingand sharing information. In some examples, these communicationcapabilities are used for receiving and sharing information related tobattery pack operation or, more specifically, to operation and testingof individual cells assembled into the packs. Some examples of thisinformation include, but are not limited to, leakage current testingresults, leakage current testing protocols, power compensationprotocols, cell operating protocols (e.g., for particular leakagecurrent and/or degradation mode results), outlier (or unsafe) cellidentification, degradation-mode determination protocols (e.g.,described below with references to FIGS. 5A-7B), fault reaction, andothers. This information may be collectively referred to as batterydata.

In some examples, the battery data (from multiple different powersystems) is aggregated to perform data analysis for multiple differentbattery cells, multiple different power packs, and/or multiple differentpower systems. The aggregate data analysis has multiple additionalbenefits in comparison, e.g., to the data analysis of an individualcell. For example, an aggregate data analysis may involve data fromcells having different cycle lives, which provides various insights intocell aging (e.g., changing in leakage current over the operatinglifetime). In another example, an aggregate data analysis may involvedata from cells operated at different parameters (e.g., charge rates,temperatures, cutoff voltages), which provides insights into effects ofthese operating parameters on the SOH and/or SOS of the cells. Otherexamples of aggregate data analysis are also within the scope. Ingeneral, information about one set of battery cells (and battery packsformed from these cells) may be relevant for another set of batterycells. For example, battery cells in both sets may be of the same type.

Overall, aggregate battery data and aggregate data analysis may be usedto identify unsafe cells and cells with reduced performancecapabilities, identify ways of mitigating risks and performancedegradation associated with these cells (e.g., taking cells offline,developing new operating protocols/strategies), new test protocols, newbattery cell and/or pack designs, and others. For purposes of thisdisclosure, the sharing of battery data among different power systems isperformed within a battery ecosystem. A battery ecosystem may be managedby a manufacturer of power systems (e.g., electric vehicles), aconsortium of different manufacturers, a third party, and others.

FIG. 1A is a schematic illustration of battery ecosystem 103, inaccordance with some examples. Battery ecosystem 103 comprises powersystem 101 and, optionally, one or more additional power systems. Eachof these power systems comprises at least one battery pack. For example,FIG. 1A illustrates power system 101 comprising battery pack 100 and anoptional additional battery pack. Any number of packs in a power systemand any number of power systems within a battery ecosystem are withinthe scope. Battery pack 100 comprises multiple battery nodes, such asfirst battery node 110 and second battery node 120, as further describedbelow with reference to FIG. 1B.

Battery ecosystem 103 also comprises battery data system 102, which iscommunicatively coupled (e.g., via various networks and/or internet) toeach of the power systems, such as power system 101. Battery data system102 comprises battery data store 104 and battery data processing engine105. Battery data store 104 is configured to receive battery data (e.g.,results of leakage current testing) from various power systems and storethis battery data. This battery data, in battery data store 104, may bereferred to as aggregate battery data. In some examples, this aggregatebattery data comprises individual cell data (e.g., results of leakagecurrent testing of individual cells). In more specific examples, thisaggregate battery data also comprises pack level data and/or powersystem-level data.

Battery data store 104 also provides this aggregate battery data tobattery data processing engine 105 for various types of analysis, suchas deterministic analysis, outlier detection, classification, linearregression, forecasting, histogram generation, and others. In someexamples, battery data processing engine 105 comprises a self-learningmodule.

In some examples, battery data processing engine 105 is configured togenerate/revise battery operating protocols and/or battery testingprotocols, as further described below with reference to FIG. 2A. Forexample, battery data processing engine 105 may revise a previously-usedbattery operating protocol based on the results of a recent leakagecurrent testing.

In some examples, these battery operating protocols and battery testingprotocols are transmitted to various power systems and used by the powersystems for operating and testing batteries, e.g., determining leakagecurrent describe below with reference to FIG. 2B.

Battery Pack Examples

FIG. 1B is a schematic illustration of battery pack 100 configured forin-situ leakage current testing of battery cells in battery pack 100, inaccordance with some examples. Battery pack 100 comprises at least twobattery nodes, e.g., first battery node 110, second battery node 120,and third battery node 130. Each battery node comprises at least onecell. As such, battery pack 100 may be referred to as a multi-cellbattery pack. In some examples, battery pack 100 comprises tens,hundreds, and even thousands of battery nodes. The number of nodesdepends on the desired power output of battery pack 100, the poweroutput of each battery cell, the number of cells in each node, operatingcharacteristics of node controllers in each node, and other likefactors. In the following description, references will be made primarilyto first battery node 110 and second battery node 120. However, onehaving ordinary skill in the art would appreciate that describedfeatures apply to additional battery nodes, which are optional.

Each battery node comprises a node controller and at least one batterycell. Referring to FIG. 11, first battery node 110 comprises first nodecontroller 112 and first battery cell 114, connected to and controlledby first node controller 112. More specifically, first node controller112 controls electrical connections of first battery cell 114 to theremaining components of first battery node 110. These electricalconnections may be also referred to as electrical power connections todistinguish from testing connections to first node controller 112, suchas voltage leads used to monitor the OCV or supplying a small current tofirst battery cell 114 to maintain a constant SOC during the leakagecurrent testing. Similarly, second battery node 120 comprises secondnode controller 122 and second battery cell 124, connected to andcontrolled by second node controller 122. Finally, third battery node130, if present, comprises third node controller 132 and third batterycell 134, connected to and controlled by third node controller 132.Second node controller 122 and third node controller 132 may be referredto as additional node controllers.

In some examples, at least one battery node comprises one or moreadditional batteries, which are optional. For example, FIG. 1Billustrates first battery node 110 also comprising additional firstbattery cell 116, independently connected to and controlled by firstnode controller 112. More specifically, first node controller 112controls first battery cell 114 and additional first battery cell 116,independently from each other. In some examples, first battery node 110comprises multiple battery cells, which are controlled together (e.g.,as a unit) by first node controller 112. The cells within this unit maybe interconnected in series, parallel, or various combinations of thesemethods. Similarly, second battery node 120 comprises additional secondbattery cell 126, also connected to and controlled by second nodecontroller 122, independently from second battery cell 124. While FIG.1B illustrates two battery cells in each of first battery node 110 andsecond battery node 120, each battery node can have any number ofbattery cells, e.g., one, two, three, four, or more. The number ofbattery cells per node is determined by the control capability of thenode controller at this node as well as the power ratings of the powerconverter in the corresponding node controller. Furthermore, the numberof cells in different nodes may be the same (e.g., as in FIG. 1B) ordifferent. FIG. 1B also illustrates third battery node 130, comprisingadditional third battery cell 136, also connected to and controlled bythird node controller 132, independently from third battery cell 134. Asnoted above, third battery node 130 is optional. Furthermore, if thirdbattery node 130 is present, third battery node 130 may include anynumber of battery cells.

FIG. 1C illustrates another example of battery pack 100. In thisexample, each node comprises six cells, forming three sets connected inparallel to each other. Each set comprises two cells connected in serieswith each other within the set. Specifically, first battery node 110comprises battery cells 114 a and 114 b (interconnected in series witheach other, and forming a first set), battery cells 116 a and 116 b(interconnected in series with each other, and forming a second set),and battery cells 117 a and 117 b (interconnected in series with eachother, and forming a third set). Each of these sets is connected inparallel to first node controller 112, which independently controls theoperation of each set. Similarly, second battery node 120 comprisesbattery cells 124 a and 124 b (interconnected in series with each other,and forming a first set), battery cells 126 a and 126 b (interconnectedin series with each other, and forming a second set), and battery cells127 a and 127 b (interconnected in series with each other, and forming athird set). Each of these sets is connected in parallel to second nodecontroller 122, which independently controls the operation of each set.This configuration may be referred to as a 3P/2S node. In thisconfiguration, in-situ leakage current testing may be performed on eachset or individual cells (e.g., using separate voltage leads, which arenot shown in FIG. 1C). In general, any configuration of each batterynode is within the scope. A node with multiple cells (e.g., eight cells,twelve cells) may be also referred to as a battery pack module, abattery module, a cell module assembly, or a module. The cells of eachmodule may have various types of connections with each other and acorresponding node controller. In some examples, the entire module istaken offline for testing one or more (e.g., all) cells of this offlinemodule. Alternatively, only a subset of cells in a module is takenoffline, while remaining cells remain operational.

The battery nodes are connected in series by bus 140. In more specificexamples, the node controllers of different battery nodes are connectedin series by bus 140. Individual connections of one or more batterycells, within each node, are controlled by the node controller of thisnode. The ends of bus 140 are coupled to or form battery pack terminals,such as first battery pack terminal 141 and second battery pack terminal142. During operation of battery pack 100, load/supply 190 is connectedto the battery pack terminals to supply power to battery pack 100 and/orto receive power from battery pack 100, which is collectively referredto as power output. Overall, battery pack 100 may provide a directcurrent (DC) power or an alternating current (AC) power (e.g., whenpower converters of node controllers are also configured to invert theDC power, supplied by the battery cells, to the AC power at the batterypack terminals).

Referring to FIG. 1B, battery pack 100 also comprises battery packcontroller 150, which is communicatively coupled to each nodecontroller. Battery pack controller 150 controls operation of each nodecontroller, which in turn controls the operation of each battery cell.For example, battery pack controller 150 instructs first node controller112 to discontinue the electrical current through first battery cell114, for the in-situ leakage current testing of first battery cell 114.In other words, battery pack controller 150 instructs first nodecontroller 112 to bring first battery cell 114 offline to initiate thein-situ leakage current testing of first battery cell 114. Battery packcontroller 150 also receives OCV measurements from first battery cell114, during the in-situ leakage current testing of first battery cell114 and while no current is flowing through first battery cell 114.

Battery pack controller 150 is also configured to maintain the poweroutput and the overall operation of battery pack 100 such that thispower output is not impacted by in-situ leakage current testing. Forexample, when first node controller 112 discontinues the current throughfirst battery cell 114, battery pack controller 150 also instructs firstnode controller 112 and/or one or more of other node controllers tocompensate for the power output changes associated with taking firstbattery cell 114 offline. This power compensation may be provided by abattery cell at the same node (e.g., additional first battery cell 116)and/or one or more cells at one or more other nodes (e.g., secondbattery cell 124). In some examples, multiple cells are used for thispower compensation, even when only one battery cell is taken offline.Spreading the power compensation over multiple battery cells allowsreducing the change in charge/discharge current through each cell.

In general, battery pack controller 150 is configured to select one ormore cells for this power compensation, based on various factors, suchas the pack current power output, expected power output, the SOC of eachbattery cell, power and control capabilities of a power converter ineach node controller, and others. Furthermore, the initial selection ofbattery cells (for this power compensation) may change over time, e.g.,by using additional cells for power compensation. Additional features ofbattery pack controller 150 are described below with reference to FIG.1E. Battery pack controller 150 should be distinguished from nodecontrollers, which provide a node-level control. Battery pack controller150 provides a pack-level control, e.g., synchronizing operations ofdifferent node controllers.

Referring to FIG. 1B, in some examples, battery pack 100 also comprisesbattery pack sensors 180, communicatively coupled to battery packcontroller 150. Some examples of battery pack sensors 180 include butare not limited to one or more thermocouples (e.g., thermally coupled toindividual battery cells), Hall effect sensors, voltage probes (e.g.,electrically coupled to terminals of each battery cell), current shunts,ultrasound sensors, pressure sensors, magnetic sensors, piezo sensors,gas sensors, and others. In some examples, the output of the sensors maybe used to trigger in-situ leakage current testing (e.g., when a batteryis at a particular voltage and/or temperature). Furthermore, the outputof the sensors (e.g., voltage probes) may be used to collect the OCVdata during in-situ leakage current testing and/or supplement the OCVdata. For example, the temperature data obtained by a thermocouple maybe correlated with the OCV data (and, optionally, with other batterydata), e.g., for the local analysis by battery pack controller 150and/or for the global analysis by battery data system 102. In someexamples, the process involves developing a weighted temperature costfunction that when combined with time and OCV readings, allows a moreprecise correlation of OCV changes/leakage current (relative to anexample not accounting for temperature).

The architecture of battery pack 100, described above and schematicallyshown in FIG. 1B, enables various functions and other features, whichare not available in conventional battery packs (with direct in seriesand/or parallel connections among battery cells). As noted above, thisarchitecture allows in-situ leakage current testing of individualbattery cells, while battery pack 100 remains operational. This testingis performed without any impact to the overall pack power output.Furthermore, this architecture allows interconnecting in series a largenumber of battery nodes, without individual cells' performancescompromising the performance of the overall pack. The performance ofeach cell is maximized by periodic and individual testing of each cell,e.g., for leakage current. The test results are used, for example, touniquely operate each cell.

A brief description of node controllers, used in battery pack 100, ispresented herein to provide additional detail of the individual cellcontrol. In some examples, a node controller comprises a powerconverter, which provides DC-DC conversion and/or DC-AC conversionfunctionality for each cell connected to the power converter. Forexample, the power converter may be configured to step-up or step-downthe voltage of first battery cell. The node controller is configured totake offline and bring online each battery cell in this node, e.g.,either individually or as a set (e.g., when multiple cells in the samenode are connected in series). A node controller also determines, basedon the input from the battery pack controller 150, the contributionlevel of the cell current to the node current. This contribution iscontrolled using, e.g., the duty cycle of the power converter in thenode controller, which provides a voltage conversion from the cell levelto the node level.

Due to the in-series connections of the nodes, the current flowingthrough each node is the same (I_(BUS)=I_(NODE1)=I_(NODE2)= . . . ). Thebus voltage is the sum of all node voltages(V_(BUS)=V_(NODE1)+V_(NODE2)+ . . . ). However, the cells arefunctionally isolated from bus 140 by their respective node controllers.The architecture of the battery pack shown in FIG. 1B allows the cellvoltage and the cell current to be different from the corresponding nodevoltage and the node current. As noted above, this difference isdetermined by the duty cycle of the power converter. Assuming negligiblepower losses at the node controllers, the combined power output of allcells in the node (e.g., P_(CELL)=V_(CELL)×I_(CELL)+V_(CELL)×I_(CELL)for the two-cell example) is the same as the power output of the node(P_(NODE)=V_(NODE)×I_(NODE)). In other words, the relationship betweenthe cell voltage and the cell current as well the node voltage and thenode current are as follows:V_(CELL)×I_(CELL)+V_(CELL′)×I_(CELL′)=V_(NODE)×I_(NODE). When a node hasonly one cell, this equation reduces toV_(CELL)×I_(CELL)=V_(NODE)×I_(NODE).

The node current is determined by the overall power output of batterypack 100, e.g., determined by load/supply 190 connected to battery pack100. When no electrical current is flowing through the cell (I_(CELL)=0)and there are no other cells in this node, the voltage across the nodeis also zero (V_(NODE)=0). With additional cells at the node, thevoltage across the node may be maintained, fully or partially, by theseother cells.

Continuing with the single cell per node example, in some examples, theentire node current is flowing through the cell (I_(CELL)=I_(NODE)). Inthese examples, the voltage across the cell is the same as the voltageacross the node (V_(CELL)=V_(NODE)), and the node controller is operables a simple connector between the cell and bus 140. In other examples,the cell voltage is different from the node voltage (e.g.,V_(CELL)<V_(NODE) for a step-up conversion or V_(CELL)>V_(NODE) for astep-down conversion).

Continuing with the single-cell per node example, when a cell is takenoffline and no electrical current is flowing through this cell(I_(CELL)=0), e.g., for in-situ leakage current testing, one or moreother nodes compensate for any power changes associated with thisoffline switch. This may be referred to as global power losscompensation or external power loss compensation across multiple nodesin battery pack 100.

With multiple cells present at the same node, the node controllerindependently controls each cell or a set of the cells (e.g., whenmultiple cells in the same nodes are connected in series). The combinedpower output of multiple cells is the same as the power output of thenode (P_(NODE)=P_(CELL1)+P_(CELL2)+ . . . ). The relationship betweenthe cell voltages and the cell currents as well the node voltage and thenode current are more complicated than, e.g., in the previous examplewith a single cell per node. With multiple cells, this relationshiptakes the following form:V_(NODE)×I_(NODE)=V_(CELL1)×I_(CELL1+)V_(CELL2)×I_(CELL2)+ . . . .

In this example with multiple cells per node, when one cell is takenoffline and no electrical current is flowing through this cell(I_(CELL)=0), one or more other cells at this node may entirelycompensate for any power changes associated with taking the first celloffline. This may be referred to as a local power loss compensation.Alternatively, one or more other nodes compensate for any power changesassociated with taking the first cell offline, even for the multiplecells per node example. Finally, the power compensation may come fromboth within the same node (e.g., other cells) and one or more othernodes, which may be referred to as hybrid power loss compensation.

FIG. 1D is a schematic illustration of node controller 160 used forcontrolling a single battery cell, in accordance with some examples.Node controller 160 represents any one of power converters shown in FIG.1B. Node controller 160 comprises one or more switches 161, which may bea field-effect transistor (FET) switch as, for example, is shown in FIG.1D. Each switch is configured to connect and disconnect a correspondingbattery cell from bus 140. It should be noted that the battery cells andbus are shown in FIG. 1D for context and these components are not partsof node controller 160. In some examples, one or more switches areconfigured to bypass an electrical current through the first batterynode 110.

In some examples, node controller 160 comprises bias and oscillatormodule 164. The bias part of this module sets the internal fixed voltageand current levels for other parts of node controller 160 (e.g., forcontrolling switches 161). The oscillator part provides a configurableclock signal for other parts of node controller 160, such ascommunication, FET switching, and analog-to-digital converters (ADCs).In some examples, node controller 160 comprises μ-Controller 165, whichcoordinates various node operations. Specifically, μ-Controller 165 isconfigured to execute the embedded control logic (e.g., software,firmware). In some examples, node controller 160 comprises communicationmodule 166, which handles communication with other nodes and batterypack controller 150. In some examples, node controller 160 comprisescontrol loop 163, which is configured to adjust switchingcharacteristics of power conversion stage 162, e.g., to regulate thedesired node output voltage and power. A combination of power conversionstage 162 and control loop 163 may be referred to as a power converter.

In some examples, node controller 160 comprises battery protection unit(BPU) and fault handling module 167. BPU and fault handling module 167is configured to monitor the battery voltage and voltage conversionlevels as well as corresponding currents. In some examples, BPU andfault handling module 167 is also configured to monitor temperatures ofvarious components of node controller 160 and battery cells. Monitoringvarious other abnormal states of node controller 160 is also within thescope. In some examples, BPU and fault handling module 167 is configuredto trigger various corrective actions (e.g., trigger a bypass). In someexamples, node controller 160 comprises power conversion stage 162,which steps up or down the voltage level from the cell-side to thebus-side. In some examples, node controller 160 comprises telemetrymodule 168, which is configured to process various measurements (e.g.,ADCs, voltage, current, temperature). Telemetry module 168 may alsoreport the measurements to control loop 163, BPU and fault handlingmodule 167, and external devices (e.g., battery pack controller 150)using communication module 166. In some examples, the quiescentoperating current of node controller 160 is at least 10 times, 100times, or even 1,000 times lower than a typical leakage current ofbattery cells. This much lower leakage current is achieved by using ADCswith large input impedance and/or by sampling the voltage infrequently(e.g., a 1-second measurement every hour). For example, a self-dischargeof 1% SOC per month for 100 Ah cell corresponds to a leakage current ofabout 1.4 mA. In this example, the ADC bias is about 10 μA to 100 μA or40 kΩ to 400 kΩ impedance to achieve the 10-100× factor.

FIG. 1E is a schematic illustration of battery pack controller 150, inaccordance with some examples. Battery pack controller 150 comprisesmemory 151, configured to store various criteria for initiating in-situleakage current testing, test protocols 152 (e.g., starting SOC,duration, desired precision), power compensation protocols 153,operating protocols 154, and test results. Some examples of thesecriteria include, but are not limited to, duration since the last test,exceeding certain threshold parameters (e.g., thresholds forcharge/discharge currents, upper/lower temperatures) during celloperation, and others. Other examples are described below.

Battery pack controller 150 also comprises processor 155, which isconfigured to initiate in-situ leakage current testing. Processor 155 isalso configured to determine leakage current, e.g., based on multipleOCV data points over time, which may be referred to as an OCV profile oran OCV function, e.g., OCV(t). For example, battery pack controller 150is configured to obtain two or more OCV values from first battery cell114 while the external cell current is discontinued through firstbattery cell 114 thereby determining the leakage current of firstbattery cell 114.

For example, processor 155 may utilize a lookup table in memory 151 tocorrelate OCV values with SOC values and then determine the leakagecurrent based on the states of SOC values over time. As noted above, aloss of 1% SOC per month for 100 Ah cell corresponds to a virtualconstant leakage current of about 1.4 mA. In some examples, processor155 is also configured to determine an operating mode for a batterycell, e.g., based on the leakage current results. For example, processor155 may instruct a corresponding node controller to disconnect the cell(e.g., after a slow discharge at less than 0.1 C) if the leakage currentresult exceeds a certain threshold (e.g., a safety threshold). Variousother functions of processor 155 are described below with reference tovarious operations of the method in FIG. 2B.

In some examples, battery pack controller 150 comprises input/output(I/O) module 156 to communicate with each node controller in batterypack 100, battery pack sensors 180, and/or external systems (external tobattery pack 100). For example, battery pack 100 may be a part of alarger system, such as an electric vehicle, grid-attached or off-gridenergy storage system, and others as described above with reference toFIG. 1A. In the examples, I/O module 156 is configured to communicatewith a battery data system, described above, to deliver test data,retrieve test protocols, and/or obtain new operating protocols.

In some examples, battery pack controller 150 is configured toproportionately or disproportionately distribute the pack power outputamong different nodes. This power distribution may be based on state ofhealth and/or state of safety parameters from this system, modelparameters learned from other systems, and other parameters.Furthermore, in some examples, battery pack controller 150 is configuredto perform hazardous failure detection. For example, a high leakagecurrent may be an indication of internal shorts. Some causes of internalshorts include, but are not limited to, (a) unintended conductiveparticles that penetrate the separator and short the positive andnegative electrodes and (b) growth of metallic dendrites (e.g. lithium,copper) from the negative electrode piercing through the separator. Highleakage current may be also an indication of the plating of metalliclithium on the surface of the negative electrode that causes an increasein the rate of electrolyte reduction. In some examples, a high leakagecurrent may be an indication of an overcharge condition that causes anincrease of the rate of electrolyte oxidation at the surface of thepositive electrode and/or over-temperature conditions that cause anincrease of the rates of electrolyte oxidation at the surface of thepositive electrode and electrolyte reduction at the negative electrode.This higher-rate electrolyte oxidation is partly due to the Arrheniuslaw governing chemical reactions and partly due to the decomposition ofthe pre-existing passivation layers at certain elevated temperatures.Some other examples of hazardous conditions, which may be evident basedon an increase of leakage current include, but are not limited to,physical damage to the cell (e.g., puncture, crushing) and externalshorts, due to the presence of foreign conductive matter between theexternal tabs of the cells or anywhere along the electrical networkconnected to the cell. Some examples of determining hazardous conditionsand corresponding degradation mode determination protocols are describedbelow with reference to FIGS. 5A-7B. For example, severe shorts can bedirectly evident from a significant increase in the leakage current ofthe cell, relative to other cells. These shorts can generally bedetermined at any SOC. Other degradation mechanisms may be less evident.For example, machine learning algorithms may be used, e.g., trained onfleet-wide cell leakage data to determine various types of degradationmechanisms.

In some examples, battery pack controller 150 is configured to performcell degradation analysis. This analysis may involve an estimate of theleakage current (or a rate of self-discharge) by monitoring theevolution of the cell voltage under open-circuit conditions over aperiod of time. Estimates of leakage current exceeding a presetthreshold or qualifying as an outlier (e.g., based on the histogram ofcomparable cells) provide various indications of cell degradation.

Examples of Global Data Analysis

FIG. 2A is a process flowchart corresponding to method 200, representingvarious examples of global battery data analysis. This global batterydata analysis may be performed by battery data system 102 or, morespecifically, by battery data processing engine 105, various examples ofwhich are described above with reference to FIG. 1A. The global batterydata analysis is performed, for example, in addition to or instead of alocal battery data analysis at a battery pack level (e.g., performed bya battery pack controller). In some examples, the results of batterypack controller analysis (e.g., the leakage current is determined usinga battery pack controller based on OCV changes over time) are suppliedto battery data system 102 as battery data for further processing.

In some examples, method 200 comprises receiving (block 202) batterydata from one or more power systems. Some examples of the battery datainclude, but are not limited to, leakage current, temperature, operatingparameters and history (e.g., several charge-discharge cycles, cut offvoltages, SOCs, and charge/discharge rates) and others. The battery datacorresponds to specific battery nodes (e.g., based on the identificationof each node) and, in some examples, is separated into sets (e.g., eachset corresponding to one node). For example, each node may have uniqueidentification in battery ecosystem 103. The battery data may beencrypted, compressed, and/or other preprocessed (e.g., identifyingvarious degradation mechanisms) before transmitting from the powersystems to battery data system 102. For example, the received batterydata comprises various determinations made at the battery pack level,such as state of health, state of power, and/or state of safety. Thisbattery data may represent different power systems, different batterypacks, and different battery cells. In some examples, the battery datamay represent the same type of cells (e.g., cells having the samedesign) or different types of cells. The selection of different datasets, representing different battery nodes, (e.g., for aggregateanalysis, benchmarking, and/or comparison) and/or data sets,representing the same battery node but at different test times, isperformed at battery data system 102. For example, leakage current datafrom a set of different size cells may be compared to determine theeffect of the cell size on self-discharge characteristics. In someexamples, battery manufacturers produce multiple cell designs (e.g., an11-Ah cell and a 55-Ah cell) using the same type of cell components(e.g., electrodes, electrolytes). The knowledge derived from one celltype may be relevant to another cell type. In some examples, batterydata is received as a continuous stream of semi-structured data.

In some examples, power system 101 is configured for wired/wirelesstransfer (e.g., secure communication channels) of battery data to abattery data system. Power system 101 or, more specifically, eachbattery node may have a unique identifier (UID), which may be a vehicleidentification number for electrical vehicles (EVs). Furthermore, powersystem 101 may include an application programming interface (API) keyfor identity authentication. When power system 101 is connected tobattery data system 102, power system 101 uploads structured data (e.g.,adhering to a schema, such as tabulated or SQL database) or unstructureddata (e.g., records pairs). In some examples, battery data is aggregatedinto an array form. More specifically, the data may be aggregated basedon a node id and/or sorted by chronological order. In some examples, asubset of the most recent data (e.g., last week, last month) is selectedfor trend analysis. The battery data is stored in battery data store104, which may be a database, specifically configured for the batterydata.

In some examples, method 200 comprises selecting (block 204) the batterydata received from different power systems, e.g., based on the celltype, temperature, age, SOC, battery application (e.g., grid,residential, EV), and other like parameters. For example, battery datafrom different nodes or even different power systems may be used tocompensate for differences among cells and provide for meaningfulcomparison. This operation may involve various data sorting algorithms.

In some examples, method 200 comprises processing (block 206) theselected battery data to determine degradation mechanisms and/orgenerate battery operating protocols, future battery testing protocols,and other like protocols. Determining degradation mechanisms based onleakage current data is described elsewhere in this document. Globalbattery data helps with finding data trends and/or applying variouspredictive models to anticipate degradation before any correspondingfailures occur and to utilize various preemptive measures to avoid thesefailures and/or degradation. For example, a cell with an increasedleakage current may be switched to an operating protocol withcell-preserving operating parameters (e.g., smaller charge/dischargecurrents, different cut off voltages, and others).

In some examples, self-learning methodologies (e.g., machine-learning,deep-learning, or even multi-modal machine-learning) are applied toprocess the data and, more specifically, to develop new battery testingprotocols and/or to revise previous test protocols. For example, initialleakage current data may be used to identify an initial degradationmechanism, which is verified using a revised test. One example of thisfeedback-loop testing is adaptive charging, where leakage current datais collected at different charging schema (e.g., fast charging of 10 Cvs. normal charging of 1 C).

In some examples, processing the selected battery data involves anoutlier detection scheme. One specific example involves a numericoutlier technique, e.g., a numeric value beyond Q3+k*IQR, where “IQR”represents the interquartile range, “Q3” represents the third quartile,and “k” represents interquartile multiplier value. Another example ofoutlier detection is a Z-score technique, which assumes a Gaussiandistribution of the battery data with the outliers positioned in thetails of the distribution. For example, the distribution of leakagecurrents may be used, as measured within a battery pack, a subset of abattery pack, a power system, or multiple power systems.

In some examples, data processing involves one or more of businessintelligence dashboards (e.g., corresponding to product usage trends andpatterns), operational monitoring (e.g., identifying cell degradationmechanisms), anomaly detection (e.g., variations in battery data),embedded analytics (e.g., providing operators of power systems variousaccess to data and reports), and data science (e.g., advanced analyticsand machine learning for predictive testing and maintenance of batterypacks, development of new test and operating protocols, artificialintelligence (AI) development).

In some examples, method 200 comprises transmitting (block 208) thebattery operating protocols and/or battery testing protocols todifferent power systems. The selection of power systems (for newprotocol) may be based on information available to battery data system102 about these power systems. Some examples of this informationinclude, but are not limited to, types of cells, sizes and/orarchitectures of battery packs, previous test data, and others.

For example, the operation of multiple EVs generates data for each cellin these EVs. For context, a typical 10-100 kWh battery pack used forEVs may include hundreds or even thousands of individual cells. Many EVsare operated using different operating parameters (e.g.,charge/discharge rates, SOCs, temperatures). As such, individual celldata from multiple EVs frequently collected over long periods (e.g., EVoperating lifetime) can be easily characterized as “big data” or, morespecifically, “big battery cell data.” Raw data corresponding toindividual cells for multiple EVs is aggregated and processed by batterydata system 102, which may be also referred to as a “cloud”. This datais processed to evaluate degradation mechanisms and, in some examples,combined with user profiles (e.g., vehicle identification numbers,owners of EVs). Based on these determined degradation mechanisms,battery management settings are determined for each use profile ofbattery pack 100. Some examples of the raw data include, but are notlimited to, leakage currents, exposed temperatures, temperatureresponses to power take in or take out, SOCs, charge/discharge rates,impedance, resistances, capacitances, magnetic fields distribution, andtime. In some examples, leakage currents are presented as a function oftemperature, SOC, and time as well as degradation mechanisms whenpreprocessed at the system level. For example, during this dataanalysis, lithium plating is detected for a certain user profileassociated with a high performance (e.g., high charge/dischargecurrents) but a smaller used range defined by the SOC. Based on thisdegradation mechanism, battery pack 100 is instructed to use lower cutoff voltages for the suspect batteries, to operate in low impedanceregimes, and/or to manage the cutoff voltages based on the celltemperature (e.g., reduce an upper cut off voltages at low temperaturesto mitigate further lithium plating).

Furthermore, individual cell data (from multiple EVs) provides higherstatistical accuracy than, for example, data available at the EV levelor just a few test cells. In some examples, this big battery cell datais used to generate more precise maintenance requirements or lifetimepredictions of the individual EVs, battery packs, and even individualcells. Self-learning cloud-based processing is used, for example, toimprove individual battery pack management. In some examples, thisbattery pack is customized for each user and may involve independentmanagement of each cell in a battery pack. Furthermore, this big batterycell data may be used to improve the manufacturing of battery cellsand/or battery packs. For example, a first cell generation is used in anEV fleet, for which the big battery cell data is collected. Based on theglobal analysis of this data, a second cell generation is developed.Additional developments of battery cycles with these feedback loops arewithin the scope.

In some examples, cell data collected from a fleet of EVs (e.g.,corresponding to a specific make-model) allows for faster dataprocessing and real-time battery management of these EVs. For example,cell data may be used for a prediction of range, charge requirement forthe next trip (e.g., full charging, partial charging, charging in acertain cut off voltage range), and power requirements, all of which maybe more precise than currently available. For example, an upcoming tripis short but requires lots of power (e.g., driving up a steep hill or athighway speeds). In this example, the battery pack of this particular EVis charged to a certain SOC while the power and efficiency are optimizedduring the utilization of this power. In another example, a degradationmechanism, identified in one or more EVs, is used to update operatingparameters of battery packs of the entire EV fleet.

In some examples, individual cell data is collected from multiplestationary storage systems. This cell data is processed in the cloud todetermine various degradation mechanisms. Based on these degradationmechanisms, battery management is updated. For example, a specificsystem is used to achieve high power peaks without requiring a largestorage capacity. If a lithium plating is detected in this system (e.g.,based on an increase of leakage currents), the operating mode of thissystem may be updated to use lower cut off voltages (than before).Furthermore, the system may be operated in low impedance regimes. Insome examples, the cut off voltage used for the operation of this systemmay be temperature-dependent (e.g., reducing upper cut off voltages atlower temperatures to mitigate further lithium plating).

In some examples, a stationary battery system is used for power storagefrom a solar array or a wind farm. In these examples, the analysis ofindividual cell data is combined with the weather forecast (e.g.,sunlight intensity and duration, wind speed), charge requirement tosatisfy energy profile for an upcoming next period (e.g., full charging,partial charging, charging in a certain cut off voltage range), and/orpower requirement.

In some examples, method 200 involves presenting results of the dataanalysis (block 210) to one or more users in battery ecosystem 103.These users may be power system manufacturers, power system owners,and/or third parties (e.g., researchers). For example, battery datasystem 102 may provide a user interface for controllably accessing,retrieving, managing, and/or analyzing the battery data. In someexamples, battery data system 102 is configured to manage the batterydata ownership and/or data accessibility.

Examples of In-Situ Leakage Current Testing

FIG. 2B is a process flowchart corresponding to method 230 for in-situleakage current testing of battery cells in battery pack 100, inaccordance with some examples. Various details and examples of batterypack 100 are described above with reference to FIGS. 1B-1E.

In some examples, method 230 comprises discontinuing (block 232) theexternal current through at least first battery cell 114. The externalcurrent may be also referred to as a current cell (I_(Cell1)=0) andshould be distinguished from the node current and the leakage current.In other words, first battery cell 114 is taken offline and no longercontributes to the power output of battery pack 100. In more specificexamples, multiple battery cells are taken offline at the same time forsimultaneous leakage current testing. For example, FIG. 1C illustratestwo battery cells connected in series (battery cell 114 a and batterycell 114 b) and disconnecting the external current through one of thesecells will also cause the same disconnecting the external currentthrough the other cell. Overall, multiple battery cells, which aresimultaneously taken offline, may be a part of the same node and/ordifferent nodes. The number of battery cells, which can besimultaneously taken offline, depends on the current power output ofbattery pack 100, SOC of the cells, and other like factors.

The operation represented by block 232 is performed while battery pack100 remains operational and, in more specific examples, while batterypack 100 provides power output (such being discharged or charged). Inother words, battery pack 100 remains online, while first battery cell114 is taken offline. Specifically, at least one other battery cell ofbattery pack 100 continues to charge or discharge, contributing to thepower output of battery pack 100 while first battery cell 114 remainsoffline.

In some examples, the external current through first battery cell 114 isdiscontinued using first node controller 112, e.g., one or more switchedof first node controller 112. More specifically, first node controller112 performs this operation based on instructions received from batterypack controller 150.

In some examples, first node controller 112 may comprise a bypass switch(e.g., as a standalone component or as a part of a power converter). Inthese examples, discontinuing (block 232) the external cell currentthrough first battery cell 114 comprising bypassing (block 233) a nodecurrent through a bypass switch or a power converter of first nodecontroller 112 as further described below with reference to FIGS. 2C-2E.

Some examples of the trigger for this operation (represented by block232) include, but are not limited to, an age/calendar time (e.g., timesince cells have been manufactured), cycle count, and previous operatingparameters and history (e.g., exposure to a high/low temperature,subjecting to a charge/discharge current) of either first battery cell114 and/or of battery pack 100. For example, a battery cell may bebrought offline and tested weekly and/or after every 50-100 cycles(since the last test). In the same or other examples, another trigger ison the SOC of first battery cell 114, e.g., the SOC of at least 70%, atleast 80%, at least 90%, or even at least 95%. A particular SOCthreshold or range is used, for example, to detect a specificdegradation mechanism, to have some charge available when the state isbrought back online, and other reasons. For example, the leakage currentmay be more evident at a higher SOC. Overall, discontinuing the externalcell current through first battery cell 114 is performed when the SOC offirst battery cell 114 is within a predetermined range, various examplesof which listed above. Various methods of measuring or estimating theSOC of first battery cell 114 are within the scope, e.g., based on ameasured voltage (e.g., an OCV or under a given load) of first batterycell 114.

In some examples, the cell temperature may be used as a condition and/oras a trigger. For example, leakage current testing is initiated when thecell reaches a certain temperature, which may be referred to as a testtemperature. As described below, the temperature is a major factoraffecting leakage current in battery cells. Therefore, a specific testtemperature may be needed to ensure meaningful leakage-current data. Itshould be noted that once the cell is taken offline, the testtemperature depends on the temperature of surrounding components (e.g.,other cells, a thermal management system of battery pack 100, and theambient environment) and the heat transfer between the cell and thesesurrounding components. In some examples, the temperature of thesesurrounding components may be controlled and/or predicted (e.g., fromhistorical data). In some examples, an elevated (e.g., greater than 40°C.) temperature is used for faster testing. Furthermore, at elevatedtemperatures, the surrounding cells will have a higher power outputcapability for power balancing and, potentially, enabling testing morecells at the same time.

Some illustrative examples include, but are not limited to: (a) after abrief or prolonged exposure to a high ambient temperature (e.g. >50° C.)or a high internal cell temperature (high current), leakage currenttesting is scheduled to detect damaged passivation layers; (b) after acharging event under low-temperature conditions (e.g. <10° C.), leakagecurrent testing is scheduled to detect lithium plating; (c) after achange in other measurable battery parameters (e.g., impedance,pressure) obtained by other monitoring techniques, leakage currenttesting is scheduled to detect physical damage (e.g. crushing) orelectrical fault.

In some examples, the operation represented by block 232 is initiatedbased on input received by battery pack 100 from battery data system102, communicatively coupled to battery pack 100. For example, batterydata system 102 provides a trigger point and/or a battery test protocolto battery pack 100 or, more specifically, to battery pack controller150, which initiates method 230 based on this battery test protocol.This trigger may be generated based on battery data obtain from otherbattery cells, e.g., which are similar to the tested battery cell ofbattery pack 100.

Overall, a starting time for discontinuing the external cell currentthrough first battery cell 114 may be determined based on at least oneof the operating history of first battery cell 114, the operatinghistory of battery pack 100, the testing history of first battery cell114, the testing history of battery pack 100, the SOC of first batterycell 114, the SOC of the battery pack (100), the temperature of firstbattery cell 114, the OCV of first battery cell 114, the voltage offirst battery cell 114 under a given load, and/or a test data analysisof battery cells equivalent to the first battery cell 114. For example,the test data analysis or, more specifically, a test protocol, developedbased on this test data analysis may be received by battery pack 100from battery data system 102. Battery pack controller 150 then uses thistest data analysis/test protocol to trigger the leakage current testingof first battery cell 114 and/or other cells of battery pack 100.

FIGS. 2C-2E are schematic block diagrams illustrating different examplesof battery pack 100, while testing first battery cell 114 for leakagecurrent. Specifically, FIG. 2C and FIG. 2D illustrate examples whereeach node controller comprises a power converter, selectively connectedto each cell of that node and also to bus 140. In FIG. 2C, each node hasonly one cell, e.g., first battery node 110 comprises first battery cell114, second battery node 120 comprises second battery cell 124, thirdbattery node 130 comprises third battery cell 134. When the externalcell is disconnected through first battery cell 114, e.g., using aswitch of first node controller 112, the bus/pack current passes throughfirst power converter 113 of first node controller 112. First powerconverter 113 or other components of first node controller 112 canmeasure voltage of first battery cell 114 through voltage leads. In someexamples, these voltage leads may be used to pass a test current tofirst battery cell 114 (e.g., to maintain first battery cell 114 at theconstant SOC while measuring the leakage current, corresponding to thetest current). Continuing with the example in FIG. 2C, the powerconnection is retained between second battery cell 124 and second powerconverter 123 as well as between third battery cell 134 and third powerconverter 133. In other words, the external current through secondbattery cell 124 and through third battery cell 134 may be differentthan the bus current, due to step-up or step-down conversion provided byeach of second power converter 123 and third power converter 133.Furthermore, one or both of second battery cell 124 and through thirdbattery cell 134 may be used for power compensation when first batterycell 114 is taken offline for leakage testing.

Referring to FIG. 2D, each node also has only one cell, but the nodes donot have power converters. Instead, each node has a voltmeter, such asfirst voltmeter 115 of first node controller 112, second voltmeter 125of second node controller 122, and third voltmeter 135 of third batterynode controller 132. First voltmeter 115 is coupled (e.g., by voltageleads) to first battery cell 114 and can measure the voltage acrossfirst battery cell 114 regardless of the connection of first batterycell 114 to bus 140. For example, FIG. 2D illustrates a state of batterypack 100, in which first battery cell 114 is disconnected from bus 140.The bus current still passes through first battery node 110 and firstnode controller 112 using, e.g., a bypass switch. It should be notedthat battery pack 100 remains operational when first battery cell 114 isdisconnected from bus 140 and the bus current is bypassed through firstnode controller 112. The voltage across the three nodes may decrease,but an external battery inverter may provide compensation for thisdecrease. In second battery node 120 and third battery node 130, thebypass switch is open while each of second battery cell 124 and thirdbattery cell 134 is connected to bus 140 and the external/bus currentpasses through these cells.

Referring to FIG. 2E, each node has two cells, similar to FIG. 1Bdescribed above. For example, first battery node 110 comprises firstbattery cell 114 and additional first battery cell 116, eachindependently connectable to first power converter 113 of first nodecontroller 112. Specifically, FIG. 2E illustrates first battery cell 114not having a power connection to first power converter 113 (thecorresponding switch is open). However, first power converter 113 orsome other component of first node controller 112 is configured tomonitor the voltage across first battery cell 114 even in thisdisconnected state. Additional first battery cell 116 has a powerconnection to first power converter 113 (the corresponding switch isclosed), and the external current passes through additional firstbattery cell 116. Both of second battery cell 124 and additional secondbattery cell 126 of second battery node 120 have power connections tosecond power converter 123 of second node controller 122. As such,external currents pass through second battery cell 124 and additionalsecond battery cell 126, which may be the same or different. Similarly,both of third battery cell 134 and additional third battery cell 136 ofthird battery node 130 have power connections to third power converter133 of third node controller 132. As such, external currents passthrough third battery cell 134 and additional third battery cell 136,which may be the same or different. In this example, the powercompensation (due to disconnecting first battery cell 114 for theleakage current testing) may be provided by various combinations of theremaining cells.

During this operation, the node current continues to flow through firstnode controller 112 as well as other node controllers (e.g., second nodecontroller 122), which are connected in series with first nodecontroller 112. At the same time, power conversion stage 162 turns onits internal bus-side FET continuously, thereby providing a path for thebus current to flow through power conversion stage 162 or, moregenerally, through the node controller.

Furthermore, in some examples, the pack voltage across (e.g., betweenfirst pack terminal 141 and second pack terminal 142 shown in FIG. 1B)remains substantially unchanged while the cell current through firstbattery cell 114 is discontinued. More specifically, the voltage ofbattery pack 100 remains substantially unchanged based on the powercompensation provided by one or more additional cells in battery pack100. Furthermore, in some examples, the power output of battery pack 100during this operation (taking first battery cell 114 offline) remainssubstantially unchanged. For purposes of this disclosure, the term“substantially unchanged” means that the value of a parameter remainswithin the operating or allowable voltage range of load/supply 190,connected to battery pack 100. In some examples, the term “substantiallyunchanged” means that the change is less than 10%, less than 5%, lessthan 2% or even less than 1%. In general, one having ordinary skill inthe art would understand the term “substantially unchanged” based on thespecific configuration and/or application of battery pack 100.

Specifically, the pack voltage remains unchanged by operating one ormore other battery cells in battery pack 100 according to a powercompensation profile. The power compensation profile may be generated bybattery pack controller 150 (e.g., before testing first battery cell114). In some examples, the power compensation dynamically changes(e.g., revised by battery pack controller 150) based, e.g., on theoverall power demand of battery pack 100, state of other cells inbattery pack 100, and other like factors. More specifically, the powercompensation profile is applied (block 234) to one or more battery cellsin the same node (as first battery cell 114) and/or different nodes.Various power compensation profiles and examples will now be describedwith reference to FIGS. 3A-3C. Overall, the power compensation may beprovided by battery cells of first battery node 110 and/or other batterynodes. The selection of the nodes and cells for this power compensationdepends on the power output of battery pack 100, SOC of battery cells,and/or other like factors.

FIG. 3A illustrates an example where the power losses, associated withtaking first battery cell 114 offline, are compensated entirely bysecond battery node 120. This example also assumes that first batterynode 110 comprises no other battery cells, besides first battery cell114, or that these other cells are also taken offline at the same time.Furthermore, for clarity, this example assumes that battery pack 100includes only two nodes, i.e., first battery node 110 and second batterynode 120.

When first battery cell 114 is taken offline (at t₁), the initialvoltage across first battery node 110 drops to zero (V_(Node1)=V₁→0).The voltage across first battery node 110 is represented by line 301 inFIG. 3A. At the same time, the initial voltage across second batterynode 120 increases to a new value (V_(Node2)=V₂→V_(2′)). The voltageacross second battery node 120 is represented by line 302 in FIG. 3A.This new voltage value (V_(2′)) is identified in the power compensationprofile and depends on the initial voltage across first battery node 110(V_(Node1)=V₁) and the initial voltage across second battery node 120(V_(Node2)=V_(2′)). More specifically, this new voltage value isselected such that the pack voltage (line 305 in FIG. 3A) remainssubstantially the same (V_(Pack)=V₁+V₂=V_(2′)=const).

The voltage increase across second battery node 120 (from V₂ to V) isachieved by changing the operation of second node controller 122 basedon the instructions from battery pack controller 150. Specifically,battery pack controller 150 instructs second node controller 122 tooperate per the power compensation mode, supplied by battery packcontroller 150 (e.g., increasing the voltage across second battery node120). It should be noted that second node controller 122 controls theoperation of second battery cell 124, which is now also operated per thepower compensation mode. Second battery cell 124 provides a differentpower output, such that the power output change of second battery cell124 is the same (but opposite) as the power output change of firstbattery cell 114 when first battery cell 114 is taken offline.

In one illustrative example, a pack with two nodes produces 300 W andhas a bus current of 20 A and a bus voltage of 15V. The initial powercontribution of the first node is 160 W, while the initial powercontribution of the second node is 140 W. As such, the initial voltageacross the first node is 8V (160 W/20 A), while the initial voltageacross the second node is 7V (140 W/20 A). It should be noted that thevoltage of the cells in both nodes may be different from the nodevoltages dues to the step-up/step-down functionality of thecorresponding power converters. Once the cell in the first node is takenoffline for testing, the node voltage drops to 0V (assuming there are noadditional cells at the first node). The power contribution of the firstnode is now OW (20 A×0V). The second node controller is instructed toincrease the power contribution and voltage, which is not 15V across thesecond node. The power contribution of the second node is now 300 W. Theoverall performance of the battery pack remains the same (the poweroutput of 300 W, the bus current of 20 A, and the bus voltage of 15V).In this illustrative example, all power losses due to taking the cell inthe first node offline are compensated by the cell in the second node.

One having ordinary skill in the art would understand how the aboveexamples can be scaled up to additional nodes. More specifically,multiple nodes are used for power compensation when a battery cell inone node is taken offline. For example, a battery pack may include 100nodes. When a battery cell is tested in one of these nodes, and thisnode no longer contributes to the power output of the pack, batterycells in the remaining 99 modes may be used to compensate. For example,each of the battery nodes may equally contribute, e.g., 1/99 share ofthis total power compensation, which may be referred to as an even powercompensation distribution. Alternatively, power compensationcontributions from different nodes can be different, e.g., determinedbased on various cell conditions and cell operating parameters in thesenodes. Furthermore, one having ordinary skill in the art wouldunderstand how the power compensation features are used when multiplecells are taken offline, e.g., either for testing or as a result oftesting. For example, in a battery pack with 100 nodes, 5 battery cellsmay be taken offline such that the cells in other nodes (e.g., remaining95 nodes) are used for power compensation.

FIG. 3B and FIG. 3C illustrate another example, where power lossesassociated with taking first battery cell 114 offline are compensatedentirely within first battery node 110. Specifically, FIG. 3Billustrates that the voltage (line 301) across first battery node 110(V_(Node1)=V₁) and the voltage (line 302) across second battery node 120(V_(Node2)=V₂) remain substantially the same as first battery cell 114is taken offline (at t₁). Furthermore, the pack voltage (line 305)remains substantially the same (V_(Pack)=V₁+V₂). Overall, there are nochanges to second battery node 120 and no changes are observed at thepack level as a result of taking first battery cell 114 offline.

Referring to FIG. 3C, the current (line 311) through first battery cell114 drops to zero at t1 (I_(Cell1)=0). However, in this example,additional first battery cell 116, which is also a part of first batterynode 110, entirely compensates for the power changes associated withdiscontinuing the cell current through first battery cell 114. FIG. 3Cillustrates an increase of the current (line 312) through additionalfirst battery cell 116 (I_(Cell1) steps up at t₁). The level of thisincrease depends on the additional power needed or, more specifically,on the voltage across first battery cell 114 and current through firstbattery cell 114 before t₁. Briefly referring to FIG. 1D, powerconversion stage 162 disconnects one of switches 161 to take thecorresponding cell offline. At the same time, power conversion stage 162controls the other one of switches 161, connected to the remaining cell,such that the voltage output of the power converter remainssubstantially the same.

In some examples, method 230 comprises determining (block 240) theleakage current of first battery cell 114. The leakage current may bedetermined based on the cell data obtained from first battery cell 114while the external cell current is discontinued through first batterycell 114. For example, the cell data may comprise OCV changes resultingin first battery cell 114 being offline or, more specifically, an OCVprofile of first battery cell 114. However, other examples of the celldata are also within the scope, e.g., a current needed for keeping aconstant SOC of first battery cell 114. This operation may be performedby first node controller 112 and/or by battery pack controller 150.Furthermore, in some examples, the leakage current of first battery cell114 is determined externally (e.g., battery data system 102), in whichcase the cell data (e.g., the OCV changes) is transmitted externally.

In one illustrative example, a tested cell is initially charged to 30%SOC of the total capacity. The cell is kept offline for 1 week (168hours). The test is performed at 20° C. An OCV drop during this periodis 0.2 mV, which corresponds to 0.02% SOC decrease (from the initial 30%SOC). Based on the capacity of this cell, this 0.02% SOC decrease over168 hours corresponds to the leakage current of 0.1 mA. In someexamples, the leakage current is expressed in terms of capacity, e.g., 1C corresponding to going from 0% to 100% SOC in one hour. Based on thisdesignation, the leakage current in the above example is 1.2×10⁻⁶ C.

One example of the OCV profile is shown in FIG. 4A. The OCV profilespans over a sufficient period, which may depend on how evident theleakage current is (e.g., the amount of leakage current, the precisionof measuring equipment, the required accuracy, and other like factors).For example, smaller current leaks may require longer testing durationsto detect sufficient voltage drops. In some examples, the duration is atleast 24 hours or, more specifically, at least 168 hours. The durationfor OCV measurement (e.g., first battery cell 114 being offline) dependson the SOC of first battery cell 114, the temperature of first batterycell 114, and calendar age and cycle count of first battery cell 114 asfurther described below with reference to FIGS. 4B and 4C. Furthermore,the duration may depend on the precision of the measuring tools,required data precision, and the actual leakage current (e.g., a shorterduration for very leaky cells). In some examples, the period, duringwhich the OCV changes are monitored, is dynamically selected/adjustedbased on the identified OCV changes (e.g., extended if the OCV changesare not sufficiently detectable). Furthermore, this period may alsodepend on battery pack's ability to operate with first battery cell 114being offline.

Specifically, FIG. 4A illustrates voltage profiles of two cells, such asfirst battery cell 114 (V_(Cell1)—represented by line 321) andadditional first battery cell 116 (V_(Cell1)′—represented by line 322).At t₁, first battery cell 114 is taken offline, while additional firstbattery cell 116 continues to charge. At this point, the OCV of firstbattery cell 114 is at OCV₁ level. First node controller 112 obtains theOCV profile of first battery cell 114 and reports this OCV profile tobattery pack controller 150 for analysis and determining leakage currentof first battery cell 114. First battery cell 114 remains offline untilt₂ and the OCV profile may be obtained for this entire duration.

At t_(1′), additional first battery cell 116 is switched to a constantvoltage charging and continues at this mode until t_(2′), at whichpoint, additional first battery cell 116 starts discharging. It shouldbe noted that in some examples, additional first battery cell 116 may besubjected to multiple charge-discharge cycles, between t_(1′) and t_(2′)and while first battery cell 114 is tested. At t₂, first battery cell114 is brought back to the offline mode and continues to dischargetogether with additional first battery cell 116. This operation isreferred to as reestablishing the cell current through first batterycell 114 and is described below with reference to block 280.

In some examples, the duration of the leakage current measurement iscontrolled by the SOC of the tested cell and the operation of othercells in battery pack 100, e.g., cells responsible for powercompensation. Referring to FIG. 4A, the tested cell is brought onlinewhen the SOC of the tested cell matches that of other cells in batterypack 100 (e.g., the SOC corresponds to the voltage of the cell). In someexamples, a SOC level, at the time the cell is taken offline, isspecifically selected to (a) provide sufficient power back up (e.g., ahigh SOC) and/or (b) provide sufficient testing duration (e.g., increasethe time between t₁ and t₂). In some examples, other cells in batterypack 100 undergo multiple charge-discharge cycles before the tested cellis brought back online.

Overall, in some examples, determining (block 240) the leakage currentof first battery cell 114 comprises obtaining (block 242) multiple OCVdata (e.g., in the form of an OCV profile) and analyzing (block 244)this OCV data and/or leakage current data. The OCV data is obtainedusing first node controller 112 or, more specifically, voltage probesconnected to telemetry module 168. It should be noted that while the OCVdata is obtained, first node controller 112 remains disconnected frompower conversion stage 162 of first node controller 112 by keeping thecorresponding power switch open. The OCV data is analyzed by batterypack controller 150. For example, a linear regression of the OCV data,which may be referred to as OCV(t), is performed.

In some examples, method 230 further comprises monitoring (block 243)the temperature/obtaining the temperature readings of the tested cell,e.g., during the entire period of the leakage current testing. Theeffect of the temperature on leakage current is described with referenceto FIG. 4C. Therefore, in these examples, the analysis of leakagecurrent is performed in the context of the cell temperature during theleakage current testing (e.g., OCV monitoring).

Referring to FIG. 4A, in some examples, the asymptotic portion of theOCV profile (line 321) is approximated with linear trend-line 323.Specifically, this asymptotic portion is identified between periodt_(1″) and period t₂. This period may be referred to as OCV datasampling period. The slope of this linear trend-line (ΔV/Δt) representsthe rate of SOC decrease, due to the leakage current. More specifically,for a given cell capacity, the leakage current is calculated based onthe rate of SOC decrease. Alternatively, further analysis (e.g.,degradation mechanism determination) is based on the SOC change rate.

In some examples, analyzing (block 244) the OCV data comprisescharacterizing the battery cell condition and/or determining one or morepossible degradation mechanisms. For example, a leakage current is firstcalculated from the OCV data as described above with reference to FIG.4A. If the leakage current is less than a first threshold (e.g.,I_(leak)<I_(warning)), then the original operating parameters are usedfor the cell going forward. The leakage current testing is repeated,e.g., after between 10 days and 365 days or, more specifically, between14 days and 60 days. In some examples, I_(warning) is between C/20,000and C/4,000 or, more specifically, between C/10,000 and C/6,000. In someexamples, I_(warning) corresponds to (ΔOCV/Δt)_(warning) of between 0.5mV/day and 10 mV/day or, more specifically, 1 mV/day and 2 mV/day, e.g.,for lithium-ion cells.

However, if the leakage current is greater than the first threshold(e.g., I_(leak)>I_(warning)), then the leakage current is compared to asecond threshold (e.g., I_(failure_warning)). Continuing with thisexample, if the leakage current is less than the second threshold (e.g.,I_(leak)<I_(failure_warning)), then a warning is associated with thiscell. The cell may be subjected to advanced cell balancing, e.g.,voltage balancing, cell power limiting, and/or internal resistancebalancing. In some examples, I_(failure_warning) is between C/10,000 andC/1,000 or, more specifically, between C/6,000 and C/2,000. The ratio ofthe first and second leakage current thresholds (i.e.,I_(warning)/I_(failure_warning)) may be between 1.2 and 4 or, morespecifically, between 1.5 and 2.5. In some examples, I_(failure_warning)corresponds to (ΔOCV/Δt)_(failure_warning) of between 1 mV/day and 25mV/day or, more specifically, 2 mV/day and 10 mV/day, e.g., forlithium-ion cells.

On the other hand, if the leakage current is greater than the secondthreshold (e.g., I_(leak)>I_(failure_warning)), then the leakage currentis compared to a third threshold (e.g., I_(leak)<I_(severe)). Continuingwith this example, if the leakage current is less than the thirdthreshold (e.g., I_(leak)<I_(severe)), then a severe warning isassociated with this cell. The cell may be subjected to variousmitigation strategies, such as using lower charge voltage, voltagebalancing, cell power limiting, converging to the knee at the samepoint, under-voltage (UV) and over-voltage (OV) protection, higher SOC,temperature control, current protection, internal resistance, andothers. For a cell with a severe warning, a new leakage current testingmay be scheduled thereafter, e.g., 1 day to 60 days or, morespecifically, after 7 days to 30 days. In some examples, I_(severe) isbetween C/5,000 and C/200 or, more specifically, between C/2,000 andC/5,000. The ratio of the first and second leakage current thresholds(i.e., I_(failure_warning)/I_(severe)) may be between 2 and 10 or, morespecifically, between 3 and 6. In some examples, I_(severe) correspondsto (ΔOCV/Δt)_(severe) of between 5 mV/day and 100 mV/day or, morespecifically, 10 mV/day and 40 mV/day, e.g., for lithium-ion cells.Finally, if the leakage current is greater than the third threshold(e.g., I_(leak)>I_(severe)), then a severe degradation mechanism or evena failure mode is associated with this cell. The cell may discharge to alow/safe voltage (e.g., less than 3V for lithium-ion cells) and bepermanently bypassed. Overall, analyzing (block 244) the leakage currentdata may comprise setting a timeframe for a new leakage current testingfor first battery cell 114 based on the currently determined leakagecurrent.

In some examples, analyzing (block 244) the leakage current datacomprises comparing the identified leakage current (and otherconditions, if available, e.g., temperature) to known test data models.These test data models may be provided from battery data system 102.Furthermore, in some examples, analyzing (block 244) the OCV datacomprises trending the leakage current data for the tested cell overtime, which may be referred to as historical trending analysis. Forexample, the same cell may be tested (for the leakage current) multipletimes over the operating lifetime of this cell.

In some examples, analyzing (block 244) the OCV data and/or leakagecurrent data comprises comparing the data of the tested cell toreference data (e.g., average data for other cells in the same batterypack or fleet-wide data available from battery data system 102). Thereference data may be selected based on various conditions, such as celltemperature during testing, SOC during the test, and others.

In some examples, analyzing (block 244) the leakage current data (or,more specifically, the OCV data) comprises determining (block 245) oneor more degradation mechanisms and, in more specific examples, theseverity of each particular degradation mechanism. Some examples ofthese degradation mechanisms are an internal mechanical short, gasevolution, solid electrolyte interface, or metal dendrite formation. Itshould be noted that other cell characteristics (besides the OCV data)may be used for the degradation mechanism determination. For example,OCV data at a low SOC may be used for determining the decomposition ofthe electrolyte on the negative electrode. OCV data at a high SOC may beused for determining oxidation on the positive electrodes, gassingcaused by the reduction on the negative electrodes, and/or developmentof mechanical shorts inside the cell. Dendrite formation may bedetermined from OCV data at both low and high SOC. More specifically,analyzing the OC data may involve monitoring changes in the leakagecurrent at different SOC and/or after different number cycles.

For example, different degradation mechanisms may have one or moreunique leakage current fingerprints, which allow distinguishing amongthe degradation mechanisms, e.g., differentiate lithium plating eventsfrom internal short events and gassing events. These fingerprints willnow be described in more detail with reference to degradation-mechanismdetermination protocols. Starting with lithium plating and withreference to FIG. 5A, a leakage current caused by lithium plating (line502) tends to decrease over time, e.g., from a higher valuecorresponding to the initial leakage current (I_(L-init)) to a lowervalue corresponding to the stable leakage current (I_(L-s)). The initialleakage current is higher due to the presence of the freshly-platedlithium metal on the negative electrode. This fresh lithium triggersvarious reactions, described above, which in turn cause the leakagecurrent due to the material and electron transfer within the cell. Thesereactions consume and passivate the lithium metal, which slows thereaction rate and reduces the corresponding leakage current.

Referring to FIG. 5B, line 510 corresponds to a cell with no or minimallithium plating, which may be referred to as a healthy cell. The leakagecurrent (I_(L-Healthy)) is minimal for the most SOC range, with a slightincrease as the cell approaches a fully-charged state (i.e., SOC of100%). This increased leakage current is shown as I_(L-Healthy′) in FIG.5B. A lithium plating event of the cell is presented by line 512. Onehaving ordinary skill in the art would understand that the lithiumplating event typically occurs above a certain minimal SOC. In otherwords, the cell needs to be sufficiently charged and enough lithiumtransferred to the negative electrode for lithium plating to occur. Uponthe lithium plating and assuming the cell continues to be charged, theleakage current increases to a new level (I_(L-Plated1′)). As describedabove, freshly-plated lithium metal triggers various side reactions,resulting in an additional leakage current (ΔI_(L-Plating1)). If thecell is discharged soon after the lithium plating event (withoutallowing the plated lithium metal to passivate), then the leakagecurrent profile follows line 514. However, over time, the lithium metalpassivates and line 514 transitions into line 516, corresponding tolower leakage currents across the entire SOC range. The passivationprocess and the decrease in leakage current are described above withreference to FIG. 5A.

It should be noted that FIG. 5B illustrates an example of only onelithium plating event. If no further plating events occur, then theleakage current profile stays at line 516 or even drops down to thelevel represented by line 510. For example, a previously formed SEIlayer may be lost due to the plating while a new SEI layer may not beeasily formed. In this example, a single plating event may not bring theleakage current above the threshold value (I_(L-MAX)).

FIGS. 5C and 5D illustrate additional plating events. These events mayoccur during each charging or during charging at certain conditions(e.g., over a certain SOC level, above at a certain charge rate, whilethe cell is above a certain temperature, and others). Referring to FIG.5C, before any additional plating events, the leakage current profile isrepresented by line 516, which is the same line as in FIG. 5B. Theleakage current profile already reflects the previous plating event,described above with reference to FIG. 5B. A new lithium plating eventof this cell is reflected by line 522. Upon the lithium plating andassuming the cell is fully charged, the leakage current increases to anew level (I_(L-Plated2′)). If the cell is discharged soon after thisnew lithium plating event and without allowing the newly plated lithiummetal to passivate, then the leakage current profile follows line 524.However, over time the lithium metal passivates, and line 524transitions into line 526. In this example, this additional platingevent may also not bring the leakage current above the threshold value(I_(L-MAX)).

FIG. 5D reflects yet another plating event. Before this new platingevent, the leakage current profile is represented by line 526, which isthe same line as in FIG. 5C. The leakage current profile alreadyreflects multiple previous plating events, described above withreference to FIGS. 5B and 5C. A new lithium plating event of this cellis reflected by line 532. Upon the lithium plating and assuming the cellis fully charged, the leakage current increases to a new level(I_(L-Plated3′)). As before, if the cell is discharged soon after thisnew lithium plating event and without allowing the newly plated lithiummetal to passivate, then the leakage current profile follows line 534.However, over time the lithium metal passivates, and line 534transitions into line 536. In this example, line 534 exceeds thethreshold value (I_(L-MAX)), which may be used to take the cell offlineor adjust the operating parameters of the cell. In the same or otherexamples, a rate of increase (e.g., a sharp leakage current increase inthe same cycle or over a small number of cycles) is used as criteria toadjust the operating parameters of the cell.

While FIGS. 5A-5D illustrate an example of three plating events, onehaving ordinary skill in the art would understand that any number ofplating and/or other degradation mechanisms are within the scope. Theabove example is used to present an illustrative signature of leakagecurrent profiles corresponding to lithium plating, e.g., todifferentiate lithium plating from other degradation mechanisms. Thissignature may be used to determine if a particular cell has experiencedone or more lithium plating events from one or more leakage currentprofiles, identified during in-situ testing of the cell. Furthermore,battery pack controller 150 and/or battery data system 102 may determinea cause of these lithium plating events (e.g., cell defects) and, insome examples, develop new operating parameters for the cells to avoidfuture lithium plating.

FIGS. 6A and 6B illustrate a signature of leakage current profilescorresponding to internal shorts. Unlike lithium plating, once aninternal short occurs, the leakage current tends to remain the same overtime. Generally, there are no passivation/self-curing options forinternal short events, unlike lithium plating. However, at very highvalues of leakage currents, the leakage currents may cause changes inthe SOC, which in turn affect leakage currents. For small leakagecurrents, the SOC impact is negligible for typical test durations. Ingeneral, a leakage current, caused by an internal short, increases witha SOC as the pressure is built up between the electrodes.

Referring to FIG. 6A, line 610 corresponds to a cell with no or minimalinternal shorts, which may be referred to as a healthy cell. The leakagecurrent (I_(L-Healthy)) is minimal for the most SOC range with a slightincrease toward a fully-charged state (i.e., SOC of 100%—shown asI_(L-Healthy)). An internal short event of the cell is presented withline 612. In this example, the cell continues to charge after theinternal short event occurs, and the leakage current increases to a newlevel (I_(L-short′)). Specifically, the internal short provides newpaths for the leakage current, e.g., corresponding to Δ_(L-short1). Asthe cell is discharged, the leakage current profile follows line 614.

It should be noted that FIG. 6A illustrates only one internal shortevent. If no further short events occur, then line 614 continues torepresent the leakage current profile of this cell.

Line 614 is positioned above line 610 as the newly developed shortscontinue to provide additional paths for the leakage current incomparison to the cell before the internal short event. As shown in FIG.6A, a single plating event may not bring the leakage current above thethreshold value (I_(L-MAX)).

FIG. 6B illustrates an additional short event. Overall, one or moreshort events may occur during various operations of the cell, e.g.,charging when the internal pressure of the cell increases and the shortsbecome more evident. Referring to FIG. 6B, before an additional internalshort event, the leakage current profile is represented by line 614,which is the same profile as shown in FIG. 6A. This leakage currentprofile already reflects the previous internal short event, which isdescribed above with reference to FIG. 6A. A new internal short event isrepresented by line 622. As the cell continues to charge, the leakagecurrent increases to a new level (I_(L-short2′)). As the cell isdischarged, the leakage current profile follows line 624. In thisexample, line 624 exceeds the threshold value (I_(L-MAX)), at least atthe high SOC levels.

FIGS. 7A and 7B illustrate a signature of leakage current profilescorresponding to gassing within a battery cell. A gassing event may becaused by overcharging, by consuming electrolyte additives, and/or byreacting various catalytic materials on the positive electrode. Theleakage current signature of this degradation mechanism is typically nottime-dependent but strongly influenced by the SOC. The gassing event maybe detected by a very sharp increase in leakage current at high levelsof the SOC as, e.g., schematically shown in FIGS. 7A and 7B.

Referring to FIG. 7A, line 710 corresponds to a cell with no or minimalgassing, which may be referred to as a healthy cell. The leakage current(I_(L-Healthy)) is minimal for the most SOC range with a slight increasefor the fully-charged cell (i.e., SOC of 100%—shown as I_(L-Healthy′)).A gassing event of the cell is shown by line 712. In this example, thecell continues to charge after the gassing event, and the leakagecurrent increases to a new level (I_(L-Gas′)). As the cell isdischarged, the leakage current profile follows line 714. At low SOCvalues, line 714 may be substantially the same as line 710.

FIG. 7B illustrates an additional gassing event. Overall, any number ofgassing events may occur during various operations of the cell.Referring to FIG. 7B, before an additional internal short even, theleakage current profile may be still represented by line 710. In otherwords, there is no or minimal cumulative effects of previous gassingevents. A new gassing even is shown by line 722. As the cell continuesto charge, the leakage current increases to a new level (I_(L-Gas2′)).As the cell is discharged, the leakage current profile follows line 724.In this example, line 724 exceeds the threshold value (I_(L-MAX)), atleast at the high SOC levels.

Overall, determining (block 245) one or more degradation mechanisms offirst battery cell comprises comparing the leakage current of firstbattery cell 114 with different degradation mechanism signatures. Thesesignatures may be available at battery data system 102 based on testingof other battery cells (e.g., equivalent to first battery cell 114) atvarious conditions (e.g., temperatures) and/or previous operatinghistories (e.g., charge/discharge rates).

In some examples, analyzing (block 244) the leakage current data (or,more specifically, the OCV data) comprises determining new operatingparameters (an operating mode) for the tested battery based on thisanalyzed data. For example, the maximum charge/discharge current throughthe cell may be reduced (e.g., below one of the threshold operatingcurrent levels) if the leakage current exceeds one or more thresholdleakage current levels. In another example, the tested battery cell istaken completely offline (e.g., after a controlled discharge) if theleakage current is severe and exceeds a set threshold. The external cellcurrent through first battery cell 114 is reestablished according tothese new operating parameters. For example, the external cell currentis reestablished at a new level, different from a level, beforedetermining the leakage current.

It should be noted that the leakage current depends on the SOC,temperature, pressure, and other characteristics, which may be takeninto account when analyzing OCV changes and determining the leakagecurrent. FIG. 4B is a schematic illustration of the leakage current(I_(L)) as a function of the SOC, represented by line 330. FIG. 4C is aschematic illustration of the leakage current (I_(L)) as a function ofthe temperature, represented by line 340. As a general trend, theleakage current increase with the temperature.

In some examples, method 200 further comprises transmitting (block 250)the cell data, e.g., the data representing the leakage current of firstbattery cell 114 from battery pack 100 to battery data system 102. Asdescribed above with reference to FIG. 1A, battery data system 102 iscommunicatively coupled to battery pack 100 and is configured toreceive, aggregate, and analyze various types of cell data and packdata. In some examples, method 230 further comprises aggregating (block260) the cell data received from battery pack 100 (e.g., the datarepresenting the leakage current of first battery cell 114) withadditional cell data (e.g., additional leakage current data). Forexample, this additional cell data may represent previous testing offirst battery cell 114 and/or other cells (in the same battery packand/or different battery packs). In some examples, this additionalleakage current data is received by battery data system 102 from a fleetof power systems comprising battery packs, equivalent to battery pack100. For example, these battery packs may have the same types of cells.This aggregation operation forms at least a portion of aggregate batterydata. In some examples, battery data system 102 analyzes this aggregatebattery data (as, e.g., described above with reference to FIG. 2A).

In some examples, method 230 further comprises receiving (270), atbattery pack 100 and from battery data system 102, one or more of aleakage current testing protocol, a power compensation protocol, a celloperating protocol, or a degradation-mechanism determination protocol.For example, battery data system 102 generates one or more of theseprotocols based on a comprehensive analysis of cell data as, e.g.,described above with reference to FIG. 2A. In some examples, theseprotocols are specific and unique to first battery cell 114, e.g., basedon the cell data obtained from first battery cell 114, such as theleakage current.

In some examples, method 200 further comprises reestablishing (block280) the external current through first battery cell 114. This operationis performed while battery pack 100 remains operational. For example,other cells in battery pack 100 may continue to charge or dischargebased on the overall power output of battery pack 100. In some examples,the pack voltage and/or the pack power output remain substantially thesame while the current through first battery cell 114 is reestablished.The power compensation for this current reestablishing operation isprovided by one or more other battery cells in the pack in a mannersimilar when the external current is discontinued through first batterycell 114, which is described above.

In more specific examples, this current reestablishing operation isperformed using first node controller 112, e.g., based on instructionsfrom battery pack controller 150 and such that the bus voltage acrossthe first node controller 112 and the second node controller 122 (i.e.,V_(NODE1)+V_(NODE2)) remains substantially unchanged. In some examples,first battery cell 114 is brought back online when the SOC of this cellcorresponds to the SOC of other cells in the pack, e.g., within 10% or,more specifically, within 5% of other cells. In the same or otherexamples, first battery cell 114 is brought back online when the OCV offirst battery cell 114 is within 50 mV or, more specifically, within 10mV of the SOC of the other cells. This SOC/OCV matching helps reduce thesurge current through any cells, e.g., when cells are reconnected inparallel (in the same node) at different voltages. Furthermore, in someexamples, this current reestablishing operation involved charging ordischarging first battery cell 114 at a different rate (a higher rate ora lower rate) to match the SOC of first battery cell 114 to other cellsin battery pack 100.

In some examples, the decision regarding the operation represented byblock 280 is based on the leakage current of first battery cell 114. Forexample, if the leakage current of first battery cell 114 is above acertain threshold (e.g., more than 10 times the nominal leakage currentfor a particular battery type), then first battery cell 114 is slowlydischarged through normal operation of battery pack 100 to a SOC of lessthan 10%, after which first battery cell 114 is taken offline andpermanently remains offline. If first battery cell 114 is the only cellin the node, then the entire node is permanently bypassed.Alternatively, if additional cells are present in the node, then theswitch connected to first battery cell 114 remains open.

In some examples, reestablishing (block 280) the external cell currentthrough first battery cell 114 is performed after at least one otherbattery cell in battery pack 100 has undergone one or morecharge-discharge cycles, while external cell current has beendiscontinued through first battery cell 114. For example, battery pack100 may remain in operation and continue being charged and dischargedwhile first battery cell 114 is being tested for the leakage testing.

Referring to FIG. 2B, in some examples, method 200 comprises switching(block 282) one or more cells back from the power compensating profile.This operation is triggered simultaneously with reestablishing the cellcurrent through first battery cell 114 such that the pack output is notimpacted by bringing first battery cell 114 online.

It should be noted that a specific application of battery pack 100 mayprovide various input into leakage current test frequency, duration,starting point, and others. For example, a typical electrical vehicle ischarged overnight, with a full charge being achieved in the middle ofthe night. Alternatively, in a grid storage application (e.g., connectedto solar panels), the full charge is achieved in the mid-afternoon. Bothapplications also have predictable downtime available for leakagecurrent testing (e.g., during work hours for electrical vehicles,testing at high SOC; during the night for grid storage systems, testingas low SOC). It should be also noted that the battery pack applicationmay also impact the temperature and other conditions of cells in thebattery pack. For example, cells in a battery pack of an electricalvehicle will have a higher temperature variability than cells in a gridstorage system, which probably translates into a longer period requiredto measure changes in OCV, due to temperature-induced noise.

Referring to FIG. 2B, in some examples, method 200 comprises performing(block 290) additional tests on the same or different cells. As notedabove, the test may be retested at different SOC, temperature, and otherlike conditions, e.g., to refine the identification of differentdegradation mechanisms of these cells. For example, the external cellcurrent is discontinued (block 232) through first battery cell 114 whenfirst battery cell 114 is at a first state. The in-situ leakage currenttesting of first battery cell 114 is then repeated (loop to block 232from decision block 290) when first battery cell 114 is at a secondstate, different from the first state. The first state and the secondstate may be differentiated by one of the temperature of first batterycell 114 (e.g., first battery cell 114 being retested at a differenttemperature), the SOC of first battery cell 114 (e.g., first batterycell 114 being retested at a different SOC), and/or prior operationhistory of first battery cell 114 (e.g., first battery cell 114 beingretested after a set number of charge/discharge cycles, after beingexposed to certain operating conditions, such as charge/discharge ratesand/or temperatures).

Further Examples

Further, the description includes examples according to the followingclauses:

Clause 1. A method 230 for in-situ leakage current testing of batterycells in a battery pack 100, the method 230 comprising:

discontinuing an external cell current through a first battery cell 114of a first battery node 110 while the battery pack 100 remainsoperational and providing power output; and

determining leakage current of the first battery cell 114 based on celldata obtained from the first battery cell 114.

Clause 2. The method 200 of clause 1, wherein the first battery cell 114is connected to a first node controller 112, and wherein the first nodecontroller 112 is further connected in series or parallel with one ormore additional node controllers of the battery pack 100.

Clause 3. The method 200 of clause 2, wherein discontinuing the externalcell current through the first battery cell 114 is performed by thefirst node controller 112.

Clause 4. The method 200 of clause 3, wherein discontinuing the externalcell current through the first battery cell 114 comprises closing abypass switch of the first node controller 112 and bypassing a nodecurrent through the bypass switch.

Clause 5. The method 200 of clause 3, wherein discontinuing the externalcell current through the first battery cell 114 comprising bypassing anode current through a power converter of the first node controller 112.

Clause 6. The method 200 of any one of clauses 1-5, whereindiscontinuing the external cell current through the first battery cell114 further comprises discontinuing the external cell current throughanother battery cell of the first battery node 110, connected in serieswith the first battery cell 114.

Clause 7. The method 200 of any one of clauses 1-6, whereindiscontinuing the external cell current through the first battery cell114 is performed such that a voltage of the battery pack 100 remainssubstantially unchanged due to power compensation provided by one ormore other battery cells in the battery pack 100.

Clause 8. The method 200 of clause 7, wherein at least one of the one ormore other battery cells, providing the power compensation, is a part ofthe first battery node 110.

Clause 9. The method 200 of any one of clauses 7-8, wherein at least oneof the one or more other battery cells, providing the powercompensation, is a part of a second battery node 120, connected inseries with the first battery node 110.

Clause 10. The method 200 of any one of clauses 7-9, wherein the powercompensation provided by the one or more other battery cells in thebattery pack 100 dynamically changes while the external cell current isdiscontinued through the first battery cell 114.

Clause 11. The method 200 of any one of clauses 7-10, wherein the powercompensation is determined by a battery pack controller 150,communicatively coupled to the first battery node 110 and remainingnodes of the battery pack 100.

Clause 12. The method 230 of any one of clauses 1-11, whereindiscontinuing the external cell current through the first battery cell114 is performed when a state of charge SOC of the first battery cell114 is within a predetermined range.

Clause 13. The method 230 of any one of clauses 1-12,

wherein discontinuing the external cell current through the firstbattery cell 114 is triggered by a battery pack controller 150,communicatively coupled to a first node controller 112, and

wherein discontinuing the external cell current through the firstbattery cell 114 is triggered based on at least one of operating historyof the first battery cell 114, operating history of the battery pack100, testing history of the first battery cell 114, testing history ofthe battery pack 100, SOC of the first battery cell 114, SOC of thebattery pack 100, temperature of the first battery cell 114, OCV of thefirst battery cell 114, voltage of the first battery cell 114 under agiven load, or test data analysis of battery cells equivalent to thefirst battery cell 114.

Clause 14. The method 230 of any one of clauses 1-13, whereindetermining the leakage current of the first battery cell 114 comprisesmonitoring changes in an open circuit voltage OCV of the first batterycell 114 over a time period, while the external cell current isdiscontinued through the first battery cell 114.

Clause 15. The method 230 of clause 14,

wherein the changes in the OCV are monitored using a first nodecontroller 112, and

wherein the leakage current of the first battery cell 114 is determinedfrom the changes in the by the first node controller 112 or by a batterypack controller 150, communicatively coupled to the first nodecontroller 112.

Clause 16. The method 230 of any one of clauses 14-15, wherein theperiod is dynamically selected based on the changes in the OCV of thefirst battery cell 114.

Clause 17. The method 230 of any one of clauses 1-16, further comprisingreestablishing the external cell current through the first battery cell114 while the battery pack 100 remains operational.

Clause 18. The method 230 of clause 17, wherein reestablishing theexternal cell current through the first battery cell 114 is performedsuch that voltage of the battery pack 100 remains substantiallyunchanged based on power compensation provided by one or more additionalcells in the battery pack 100.

Clause 19. The method 230 of any one of clauses 17-18, whereinreestablishing the external cell current through the first battery cell114 is performed when a state of charge SOC of the first battery cell114 corresponding to a SOC of at least one other battery cell in thebattery pack 100.

Clause 20. The method 230 of clause 19, wherein reestablishing theexternal cell current through the first battery cell 114 is performedafter the at least one other battery cell in the battery pack 100 hasundergone one or more charge-discharge cycles, while the external cellcurrent has been discontinued through the first battery cell 114.

Clause 21. The method 230 of any one of clauses 17-20, furthercomprising determining new operating parameters for the first batterycell 114, based on the leakage current of the first battery cell 114,and wherein the external cell current through the first battery cell 114is reestablished according to the new operating parameters.

Clause 22. The method 230 of any one of clauses 17-21, wherein theexternal cell current is reestablished at a new level, different from alevel, before determining the leakage current.

Clause 23. The method 230 of any one of clauses 1-22, further comprisingmaintaining the first battery cell 114 disconnected if the leakagecurrent exceeds a set threshold.

Clause 24. The method 230 of any one of clauses 1-23, further comprisingsetting a timeframe for a new leakage current testing for the firstbattery cell 114 based on the leakage current.

Clause 25. The method 230 of any one of clauses 1-24, further comprisingcomparing the leakage current of the first battery cell 114 with priorleakage current data for the first battery cell 114.

Clause 26. The method 230 of any one of clauses 1-25, further comprisingdetermining one or more degradation mechanisms of the first battery cell114 based on at least the leakage current of the first battery cell 114.

Clause 27. The method 230 of clause 26, wherein determining the one ormore degradation mechanisms of the first battery cell 114 comprisescomparing the leakage current of the first battery cell 114 withdifferent degradation signatures.

Clause 28. The method 230 of any one of clauses 26-27, wherein the oneor more degradation mechanisms comprise at least one of an internalmechanical short, gas evolution, solid electrolyte interface, or metaldendrite formation.

Clause 29. The method 230 of any one of clauses 26-28, wherein the oneor more degradation mechanisms is further determined based on at leastone of:

temperature of the first battery cell 114 while discontinuing theexternal cell current through the first battery cell 114,

SOC of the first battery cell 114 when discontinuing the external cellcurrent through the first battery cell 114, and

operating history of the first battery cell 114 before discontinuing theexternal cell current through the first battery cell 114.

Clause 30. The method 230 of any one of clauses 1-29, further comprisingtransmitting data representing the leakage current of the first batterycell 114 from the battery pack 100 to a battery data system 102,communicatively coupled to the battery pack 100.

Clause 31. The method 230 of clause 30, further comprising aggregatingthe data representing the leakage current of the first battery cell 114with additional leakage current data, forming at least a portion ofaggregate battery data, wherein the battery data system 102 analyzes theaggregate battery data.

Clause 32. The method 230 of clause 31, wherein the additional leakagecurrent data is received by the battery data system 102 from a fleet ofpower systems comprising additional battery packs, equivalent to thebattery pack 100.

Clause 33. The method 230 of any one of clauses 30-32, furthercomprising receiving, at the battery pack 100 and from the battery datasystem 102, one or more of a leakage current testing protocol, a powercompensation protocol, a cell operating protocol, or a degradationdetermination protocol.

Clause 34. The method 230 of any one of clauses 1-33,

wherein the external cell current is discontinued through the firstbattery cell 114 when the first battery cell 114 is at a first state,

wherein the in-situ leakage current testing of the first battery cell114 is repeated when the first battery cell 114 is at a second state,different from the first state, and

wherein the first state and the second state are differentiated by oneof temperature of the first battery cell 114, SOC of the first batterycell 114, or prior operation history of the first battery cell 114.

Clause 35. The method 230 of any one of clauses 1-34, furthercomprising:

obtaining one or more temperature readings of the first battery cell 114while the external cell current is discontinued through the firstbattery cell 114; and

correlating the one or more temperature readings to the leakage currentof the first battery cell 114.

Clause 36. A battery pack 100, configured for in-situ leakage currenttesting of battery cells in the battery pack 100, the battery pack 100comprising:

a first battery node 110, comprising a first node controller 112 and afirst battery cell 114, electrically coupled to the first nodecontroller 112, wherein the first node controller 112 is configured todiscontinue an external cell current through the first battery cell 114while the battery pack 100 remains operational and providing poweroutput;

a second battery node 120, comprising a second node controller 122 and asecond battery cell 124, electrically coupled to the second nodecontroller 122;

a bus 140, electrically interconnecting the first node controller 112and the second node controller 122; and

a battery pack controller 150, communicatively coupled to the first nodecontroller 112 and the second node controller 122, wherein at least oneof the first node controller 112 or battery pack controller 150 isconfigured to determine leakage current of the first battery cell 114.

Clause 37. The battery pack 100 of clause 36, wherein the battery packcontroller 150 is configured to maintain a voltage of the battery pack100 substantially unchanged while discontinuing the external cellcurrent through the first battery cell 114.

Clause 38. The battery pack 100 of any one of clauses 36-37, wherein thebattery pack controller 150 or the first node controller 112 isconfigured to obtain two or more OCV values from the first battery cell114 while the external cell current is discontinued through the firstbattery cell 114, thereby determining the leakage current of the firstbattery cell 114 from the two or more OCV values.

Clause 39. The battery pack 100 of any one of clauses 36-38, wherein thefirst node controller 112 comprises a power converter, configured tostep-up or to step-down a voltage of the first battery cell 114.

Clause 40. The battery pack 100 of any one of clauses 36-39, wherein thefirst node controller 112 comprises one or more switches configured todiscontinue the external cell current through the first battery cell114.

Clause 41. The battery pack 100 of clause 40, wherein the one or moreswitches are configured to bypass an electrical current through thefirst battery node 110.

Clause 42. The battery pack 100 of any one of clauses 36-41, wherein thefirst node controller 112 has a quiescent operating current that is atleast 10 times lower than expected value of the leakage current of thefirst battery cell 114.

CONCLUSION

Although the foregoing concepts have been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. It should be noted that there are many alternative waysof implementing the processes, systems, and apparatus. Accordingly, thepresent examples are to be considered as illustrative and notrestrictive.

What is claimed is:
 1. A method for on-demand in-situ leakage currenttesting of selected battery cells in a battery pack, the methodcomprising: discontinuing an external cell current through a firstbattery cell of a first battery node using a first node controller,wherein: the first battery cell is selected from multiple battery cellsin the battery pack for purposes of determining leakage current, thefirst node controller is connected in series with one or more additionalnode controllers of the battery pack, the one or more additional nodecontrollers control operation of one or more additional cells in thebattery pack, and the one or more additional cells continue to charge ordischarge according to a power compensation profile to ensure that thepower output of the battery pack is substantially unchanged while theexternal cell current through the first battery cell is discontinued;obtaining cell data from the first battery cell using the first nodecontroller while discontinuing the external cell current through thefirst battery cell; determining the leakage current of the first batterycell based on the cell data; and reestablishing the external cellcurrent through the first battery cell, using the first node controllerand switching the one or more additional cells back from the powercompensation profile, using the one or more additional node controllers,such that the power output of the battery pack remains substantiallyunchanged.
 2. The method of claim 1, wherein discontinuing the externalcell current through the first battery cell is performed when a state ofcharge (SOC) of the first battery cell is within a predetermined range.3. The method of claim 1, wherein discontinuing the external cellcurrent through the first battery cell is triggered by a battery packcontroller, communicatively coupled to the first node controller, andwherein discontinuing the external cell current through the firstbattery cell is triggered based on at least one of operating history ofthe first battery cell, operating history of the battery pack, testinghistory of the first battery cell, testing history of the battery pack,SOC of the first battery cell, SOC of the battery pack, temperature ofthe first battery cell, OCV of the first battery cell, voltage of thefirst battery cell under a given load, or test data analysis of batterycells equivalent to the first battery cell.
 4. The method of claim 1,wherein the cell data comprises changes in an open circuit voltage (OCV)of the first battery cell over a time period, while the external cellcurrent is discontinued through the first battery cell.
 5. The method ofclaim 4, wherein the time period is dynamically selected based on thechanges in the OCV of the first battery cell.
 6. The method of claim 1,wherein reestablishing the external cell current through the firstbattery cell is performed when a state of charge (SOC) of the firstbattery cell corresponds to a SOC of at least one other battery cell inthe battery pack.
 7. The method of claim 1, wherein reestablishing theexternal cell current through the first battery cell is performed afterthe at least one other battery cell in the battery pack has undergoneone or more charge-discharge cycles, while the external cell current hasbeen discontinued through the first battery cell.
 8. The method of claim1, further comprising determining new operating parameters for the firstbattery cell based on the leakage current of the first battery cell, andwherein the external cell current through the first battery cell isreestablished according to the new operating parameters.
 9. The methodof claim 1, further comprising determining one or more degradationmechanisms of the first battery cell based on at least the leakagecurrent of the first battery cell.
 10. The method of claim 9, whereindetermining the one or more degradation mechanisms of the first batterycell comprises comparing the leakage current of the first battery cellwith different degradation signatures.
 11. The method of claim 9,wherein the one or more degradation mechanisms comprise at least one ofan internal mechanical short, gas evolution, solid electrolyteinterface, or metal dendrite formation.
 12. The method of claim 9,wherein the one or more degradation mechanisms is further determinedbased on at least one of: temperature of the first battery cell whilediscontinuing the external cell current through the first battery cell,SOC of the first battery cell when discontinuing the external cellcurrent through the first battery cell, and operating history of thefirst battery cell before discontinuing the external cell currentthrough the first battery cell.
 13. The method of claim 1, furthercomprising transmitting data representing the leakage current of thefirst battery cell from the battery pack to a battery data system,communicatively coupled to the battery pack.
 14. The method of claim 1,wherein the external cell current is discontinued through the firstbattery cell when the first battery cell is at a first state, whereinthe in-situ leakage current testing of the first battery cell isrepeated when the first battery cell is at a second state, differentfrom the first state, and wherein the first state and the second stateare differentiated by one of temperature of the first battery cell, SOCof the first battery cell, or prior operation history of the firstbattery cell.
 15. The method of claim 4, wherein the external cellcurrent is discontinued through the first battery cell for a period oftime selected based on at least one of the leakage current, desired testaccuracy, equipment precision, a type of the first battery cell,temperature of the first battery cell, or a state of charge of the firstbattery cell.
 16. The method of claim 1, wherein the cell data, used fordetermining the leakage current, is a charge amount used by the firstnode controller to bring a state of charge of the first battery cell toan initial state of charge at which the external cell current wasdisconnected through the first battery cell.
 17. The method of claim 1,wherein the cell data, which is used for determining the leakagecurrent, is a cell current used by the first node controller to maintaina selected state of charge over time.
 18. The method of claim 2, whereinthe predetermined range of the state of charge is selected based on oneor more degradation mechanisms.
 19. The method of claim 14, wherein thefirst state and the second state correspond to different degradationmechanisms.
 20. The method of claim 8, wherein the external cell currentthrough the first battery cell, reestablished according to the newoperating parameters, is less than a corresponding external currentthrough at least one of the one or more additional cells in the batterypack.